YouTube is a modern miracle of engineering -- no other platform on the planet hosts the scale of video it does, indefinitely, with instant access, for free
Because Google chokes the market. There could be plenty of other competitors if Google charged for it like other companies would. Google subsidized YouTube with the rest of their company's profits, not to provide us a free platform because they're so nice, but to prevent competition. As long as YouTube was free, no other companies would be able to keep up with the costs, therefore no one else would enter the market.
If this shit is so expensive, and they want money, they can gate the content like every other streaming service, and then deal with the competition that would swell up.