Take a look at the size of Wikipedia's bank account. They constantly continue to solicit for funds as though they're desperate for funds on their site despite having billions upon billions of funds, enough to last pretty much off of the interest alone.
Work in AI, eh?
So... you didn't actually look at the size of WikiMedia Foundation's bank account.
WikiMedia absolutely has enough money to run Wikipedia indefinitely if they treated their current pile of money as an endowment and just used the income from it to support the site. They don't have "billions upon billions", but they do have almost $300M, and they spend about $3M per year on hosting, and probably about that much again on technical staff to run the site, so about $6M per year. That's 2% per year. Assuming they can get a 6% average return on their assets, they can fully fund Wikipedia forever, and then some.
So, what do they do with all of the donations instead, if the money isn't needed to run Wikipedia? It funds the foundation's grant programs. Of course, you might actually like their grant programs. I think some of their grants are great, myself, and if they were honest about what they're using it for I might be inclined to give. But they're not, and the fact that they continue lying to Wikipedia's user base really pisses me off, so I don't give and I strongly discourage everyone I can from giving, at every opportunity.