Buybacks are essentially dividends. The cash went to investors who did something with it.

Did they park it in bonds over the past 10 years? I doubt it. Interest rates were ~0, VC funding was crazy, the money taps were open. They would have been less open without these buybacks.

It's not necessarily 1:1, it seems people are more willing to spend the cash on AI than they were on other things. But it's not 1:0 either.