Why is this happening?

The deportations come amid a broader cooling of ties between the UAE and Pakistan. Abu Dhabi recently demanded early repayment of a $3.5 billion financial support package, a move seen by observers as a sign of growing frustration with Islamabad.

At the same time, Pakistan’s evolving geopolitical positioning, including its engagement with Iran and perceived lack of strong response to regional tensions, has added to the unease.

In contrast, the UAE has been strengthening ties with India, deepening cooperation in trade, investment, and security. This shift highlights a recalibration of regional priorities that appears to be leaving Pakistan increasingly isolated.

https://www.moneycontrol.com/world/uae-deports-15-000-pakistanis-amid-crackdown-islamabad-s-silence-raises-questions-report-article-13909587.html

My first question would be who are these middle east eye lot, not a news outfit I'd heard of. Wikipedia has this to say, for what it's worth:

Middle East Eye (MEE) is a United Kingdom-based media website and channel that primarily focuses on news related to the Middle East, North Africa, and the broader Muslim world. Though the organisation denies it and will not disclose its funding sources, it is widely believed that the organisation is funded by the government of Qatar.

They are in competing blocks now so ties are becoming more frigid.

Pakistan signed the SMDA with Saudi Arabia and is tightening connections with Turkey and Egypt, which is one of the emerging blocks in the region. The UAE is in another emerging block with Israel, India and Ethiopia which is increasingly at odds with the former block.

As background the UAE determined that Islamists were the number one threat to the stability of their monarchies following the Arab Spring and have been supporting whatever coup or civil war faction seems most hostile to Islamists to limit their footholds in the region. So they backed the military coup in Egypt against Morsi, RSF in Sudan (RSF are Arab supremacists but not as Islamist as the SAF), southern separatists in Yemen, Somaliland in Somalia, Haftar in Libya, you get the picture. More secular leaning governments focused on small nationalisms or the like are an easier in for India and Israel to work with than big existing Islamic-leaning countries so they are natural friends as the UAE succeeding will make the environment easier for them; fragmenting Somalia and maybe flipping Sudan also makes Ethiopia more locally powerful and potentially able to access more ports so Ethiopia is on board too and has been helping the UAE in Africa. They are all announcing new deals with each other fairly regularly.

However, the UAE made enemies with the former block this way. The former countries in the Turkey-Pakistan-Saudi Arabia-Egypt block would generally rather maintain and strengthen existing relationships they have invested into rather than see the governments they work with abruptly changed or their countries torn into fragments that then may prefer to work with India, Israel etc. So many of them are supporting groups like the Somalian government, SAF in Sudan, recognized government of Yemen and so on to keep those existing governments alive - Saudi Arabia intervened quite strongly when the southern separatists had basically wiped out the recognized government of Yemen and flipped it so that the southern separatists got extinguished instead. Egypt is a bit of an odd case because it is a secular military government that was originally buddy buddy with the UAE after the UAE helped out their coup, but fragmenting Somalia and the fighting in Sudan is very alarming to Egypt. Egypt wants for Ethiopia to have strong neighbors that Egypt can work with to check Ethiopia’s ambitions since Ethiopia controls most of the flow to the Nile River that Egypt very heavily depends on for life. If allowed to grow too strong, in theory Ethiopia could one day be powerful enough to issue ultimatums for Egypt to do whatever Ethiopia wants if Egypt wants to keep drinking water. So now they are also more down on the UAE and act accordingly, ex. Egypt and the UAE together supported Haftar in Libya against the recognized government Turkey supported but now Egypt is demanding that Haftar choke off the UAE’s Libyan supply routes to the RSF in Sudan if they want to keep Egypt’s support.

They also have different approaches in dealing with Iran now. The UAE is suffering quite a lot from their Hormuz exports being blocked and getting disproportionately blasted by Iran (they are both a soft nearby target and one Iran will very gleefully let loose on with their affiliation with Israel), and the UAE want that to end ASAP with no specter of Hormuz tolling either so they want the US to go in and take out their government. Whereas in the other block although there are frictions (ex. Iran backed Ansar Allah being way stronger than Yemen’s recognized government, Iran backed former Syrian government against Turkish aligned rebels, etc.) neighbors Turkey and Pakistan don’t want instability at their borders that could cause a refugee crisis, damage their economies and encourage local separatists they are heavily moderating the sentiment of the block to trying to go for peace. Saudi Arabia is the most hawkish in that group but they have a large east-west pipeline that eases the pain more than the UAE’s smaller bypass, are a harder target and mostly further away so they can still afford to be way more patient than the UAE can.

So through this move the UAE probably wants to cause Pakistan a lot of pain and avoid getting a bunch of remittances and savings sent over to a country it is increasingly regarding as an unfriendly one. Really awful for the workers caught up in this situation and the families who rely on them.