Beyond that, Google’s dominance isn’t going away due to their own “monopoly-like” positioning, their business relationships, the inertia of their massive public adoption, all of these applied within three or four other vital areas (ie: YouTube), their ability to pivot in response to anything novel that appeared to undermine their position, no apparent stories of Google executives hosting puppy kicking parties for the entire company to Satanic Panic everyone away from their products, the problem of promising companies being acquired because the owners (VC or founder or otherwise) are happy to be bought, the general “ick” factor of someone like Facebook attempting to enter the fray, some other things none of us have ever considered, random luck, and the initial conditions of the universe.
You have to have good results against the inconceivably vast amount of content out there, you have to be easy to use, you have to be free, and you have to be able to do all of this and more for the yeeeeeears it would take to wiggle into the space and expand while resisting the pressures above. Doable, wildly improbable.