they want to suppress the developers, not users. By making it so bothersome, so many people will just stop using sources from outside google play. First they do this and at some later time they will add more hoops to it. If they manage to strangle any developers that make stuff, people will have nowhere to turn yet they cant complain either because google will have undeniable monopoly.

The delay is almost assuredly to prevent live scamming. Like a grandparent picking up a random call or text and being tricked into thinking they're a family member/bank worker/etc.

I'll admit it's annoying, and could be used by Google later to do more annoying shit.

Taking their explanations in good faith and looking at it from an customer security point of view, I can see this cutting back on some common scam types. This is kind of like how, when you go to rustdesk.com there's a giant 'YOU'RE PROBABLY GETTING SCAMMED' banner across the top of the page:

These little steps can seems pointless or annoying to us, as most of us are probably in the upper range of tech skills, but consider the average user and it starts to make a lot more sense.