Interesting, I haven't thought about it that way before. Are buybacks more volatile compared to dividends?

Buybacks are increasingly viewed as a better way to return money to shareholders, for companies, not individual shareholders. They prop up the stock obviously, but also allow greater flexibility for the company in removing what becomes an expected obligation (dividend payment). In exchange, you can have a discretionary buyback program that can fluctuate in amount over time, and is viewed as less of a bell weather for the company's health.

What is good about buybacks for investors is that you can choose how to time your sales, which can result in tax benefits. Dividends you pay tax on a schedule that might be less suitable to whatever financial massaging investors might want to engage in.

Can you do buybacks forever or just a few decades or so?

You can always split the stock if employee and executive options are not creating sufficient shares.

On top of this, execs typically have a lot of stock based compensation. So buybacks are way better than dividends for them

Dividends, in addition to creating an expectation, are also a ratchet because an ever-increasing streak of dividends is tracked as a metric to gauge the health of a company.[1] If a company wants to return one-time excess money to investors, buybacks are the only way.

[1] https://en.wikipedia.org/wiki/S%26P_500_Dividend_Aristocrats

Did relevant tax rules change recently? If not, why is this behavior new?

It’s not new, buybacks have been increasing for decades.

A bonus 1% tax on buybacks was recently added by the Inflation Reduction Act, and Biden has called for that to be increased to 4%. If the tax is high enough, more companies will go back to paying dividends.

They were legalized in 1982, so no, definitely not new. Simply put, it took norms and customs awhile to develop around using them, plus the Net Investment Tax came into effect making the tax savings more substantial.