Arguably they're buying back stock now because they believe it's undervalued. The other prevailing narrative in the media today is that corporations are too powerful and are bleeding the American consumer & worker dry. Which is it? If they're actually bleeding the American consumer dry you'd have to be an idiot not to want a piece of the action, while if they're overvalued and about to collapse there's no reason to be afraid of them.
Apple having the largest buyback amount doesn't seem to tell us a ton by itself, given that they are among the top few most valuable companies in the world.
The headline is "Dividends and buybacks now larger than the total reported earnings of the S&P 500." For that conclusion, it's absolutely relevant that Apple et al are doing the buybacks and that their market cap dwarfs many of the companies on the S&P 500 (which has a threshold of $6B to enter, vs. close to $1T for Apple). Apple deciding that they're going to return some of the cash to shareholders they've been stockpiling for the last 5ish years would dwarf the entire earnings of most of the bottom 200 stocks in the S&P 500. That's not a report on weakness or danger in the market, it's a report of what a small number of companies are doing with a large cash hoard. It's sorta like reporting that "Residents of Medina, WA lost more money to divorce in 2019 than they made in total wages" without reporting that Jeff Bezos is a resident.