My personal suspicion - which may easily be not only mistaken, but a projection of different things - is that with so vast a population on Earth, we may be in ways less likely to become, as a species and on the whole, more technologically adept. With billions of people comes the inevitability of endless hundreds of millions literally having no reason to bother with technology in any other way than to consume it with no understanding.
And while the above is still passable on Earth, it won't fly when you live in an environment which will kill you if you are not in control both of sufficient tech and a basic understanding of it, neither of which are currently at hand.
The above is also in synergy with something positive (positive in my view), which is the natural human tendency to just enjoy life when that is possible, thus not disturb the inertia as long as life can be good.
Maybe if we first advance in other fields, such as life extension (not immortality, just a considerable extention, eg a number of decades), we will at some point get enough of just trying to have a decent life (something which perhaps the majority of our species is unable to have, and those who do only enjoy for a few years) and so on graduate to a more pananthropic fondness and skill in science, math and other orders which can help increase technology to the degree needed for space colonization.
Needless to say, this is not close to where things currently stand, for we are still a species where the ability to have a nice life is rare and usually fleeting even where it - mostly by chance - seems to manifest.