Alright, you've proposed two possible pressures that may result in space colonization here.
The first one is that a lot of people want to colonize space. However I don't think that will get them anywhere. It's incredibly expensive to colonize space. A bunch of space enthusiasts can't overcome that barrier with passion alone.
The second one is overpopulation. The problem here is that space colonization is not and never was a workable solution to overpopulation for the simple reason that even if every country on Earth was launching rockets at the rate of one per minute, it still would not move humans off the Earth faster than new ones are born.
Logistics aren't much of an issue, comparatively. The technology has been around for decades.
I agree the technology exists, but expense is the barrier. It is not trivial, either. Ignoring the high cost of something doesn't make it cheaper, and even if one is able to raise the money from donors, if the project doesn't generate more income than it costs to maintain, it will not be permanent.
This is why, as I have written in the past, nearly every underwater habitat ever built was scrapped to recoup some of the cost by selling off the metal it was made out of. None were simply left in the water.
Out of the three in operation today, one is operated with university funding (Aquarius, formerly government funded) the other two are the Jules Undersea Lodge which pays for itself by hosting tourists, and Marinelab (in the same lagoon as Jules, owned by the same guy) which is supported by revenue from the operation of the Jules as a hotel.
I do not mean to be a downer. But this is the difference between dreamers and executors. The world has plenty of dreamers. It has very few people who can actually make those dreams happen, and fewer still who can make them happen in a lasting way.
This is because at the end of the day, stuff like underwater bases, space stations and so on are very expensive. It has to be paid for somehow. If it's not going to be paid for with tax dollars, then it needs to generate profits somehow to pay for itself.
I don't think overpopulation is nearly the threat many present it to be, and even if it were, I don't think space colonization would be a cure for it, just an incentive for some to pursue it.
And don't get me wrong, I don't mean to trivialize the cost of oceanic exploration or colonization either. However, since government has for the most part been behind it thus far, we don't really know what the real prices or potential innovations are in the industry waiting to be unlocked.
For the moment, I don't think sea floor habitation is likely, but The Seasteading Institute offers some interesting ideas, and this interview explores some of the ways it could generate a productive profit.