I’d like to think they’d do it out of curiosity but I suppose after the first dozen buffoons they would lose interest.

Hypothetically, having access to older gene stock could make sense. As would a source of disposable labor. Or repopulation after a catastrophe.

Plenty of reasons.

But I can about damn guarantee it wouldn't be just because they want to be nice

There might not be a future with a population problem, most countries are already below sustainable fertility rates and like every country is in decline. Young people are not having children, they cannot afford it.

Technology can enable the Earth to comfortably fit over a trillion humans, overpopulation has never been a serious direct issue, but rather it causes a lot of secondary issues. With the rise of AI and automation, we are quickly approaching a point where we will have one of two futures to pick from. Either the entire worlds biosphere gets destroyed to enrich one person(or an ai takes over, either way, this is the bad ending) or we overthrow capitalism and instill a government with strong social policies and UBI. Either way, resource scarcity isn't a problem because the rise of AI and automation means we can harvest material on scales never before seen, and we can start harvesting asteroids(a single one of earths trojan asteroids can contain more gold than has ever been mined on earth).

Assuming we go the utopia route, the first issue is water. This is solvable by various means, we can desalinate water at massive energy cost. That comes from nuclear, whether it's on earth, off earth, or coming from the original nuclear source. I'm picturing massive solar panel arrays in space near L1. These would have the benefit of beaming terawatts of power back to earth, and they can be gimbaled to control the amount of light hitting earth, thereby controlling our inevitably devastated climate either way we go. Next issue is food. GMO's and hydroponics are already set to solve this, if you're really concerned then just construct an oneill cylinder purely dedicated to growing hydroponic crops. One such cylinder combined with a space tether, rail gun, or space elevator would enable you to grow enough food to feed everyone, and easily ship it to exactly where it needs to be a minimal cost(resource cost, "finances" are made up and a product of capitalism, we got rid of money because it's literally useless now)

Next issue is housing. There is way, way, way more room on earth we can stick humans than you can possibly imagine. Earlier, I mentioned O'Neill cylinders. Those aren't on earth, so don't count towards my statement, but just one of those could comfortably house, feed, and sustain the entire current human population. We have tricks for doing similar stuff on earth though, too. You can reduce people's individual footprint by culturally or genetically editing us to be more efficient, consume less resources, etc. Imagine a million people fitting in your bedroom because they're all the size of ants, and have comparable caloric intake. We can build megastructures on earth too. There's really no limit to how high we can build, just under capitalism you have to have the funds to make it work. You eventually reach the material strength of your material, for steel I don't think you can normally build much higher than a mile before the structure weighs more than the steel can support. But we don't have to rely on the materials strength, because we have active support. There's a bunch of different ways we can do that, but the simplest, least efficient, but most intuitive way is simple: every 30 stories or so, we attach helicopter rotors to hold the weight of that section of the building. If that sounds wildly impractical, that's because it is. But that's just a proof of concept, what you would actually use is a loop of molten metal flowing at a high velocity through a constrained tube. You can make this arbitrarily long, although it exponentially increases the load on your pumps as you do so. It works the same way your hose works when you turn on full blast, the internal water pressure forces the hose to straighten out. Now imagine your hose was vertical, with thousands of times more deltaP. That holds up buildings.

What about culturally? It would seem I still haven't touched upon an actual reason to unthaw these people - but I have. Strong social systems are a prerequisite to this type of future, if we don't instill UBI soon there will be a complete economic collapse as more of the job market is taken by automation. We will have to shift away from the idea that humans have to work to survive, or we will die as a species. That sort of social understanding begets empathy, and without capitalism there is no "cost" to unthaw them. You don't build a society to harm people(well, at least I don't), you build it to help them. And if you have the medical technology and can't come up with a serious reason not to, it would seem like a massive contradiction to not thaw these people. Youve been capitalism brained into thinking people only have the value that can be extracted from them.

Wouldn’t that be true for mice as well? I wonder how they got around that for this study