The cookie cutters were replaced quickly because they were bad stadiums, not because they had reached the end of their life. RFK Stadium in Washington still acts as a soccer stadium despite being a decade older than most of the other cookie cutters that were replaced ~15 years ago. Parts of the Vet were falling apart, and cracks were all over the place at TRS, but nothing that couldn't have been fixed had anyone had any interest in extending the lives of those monstrosities.
Of course it's at the end of it's life now, but those stadiums had another 20-25 years in them if necessary...they just lacked amenities that newer stadiums had and the fans hated them. Three Rivers could have lasted another 25 years, but the Pirates wouldn't have lasted 25 more years playing in it. That's not going to be the case with any of these, but they're still being replaced for reasons other than the stadium reaching the end of its life-cycle. If not for DC United finally getting approval for a new soccer-specific stadium there was a very real chance that RFK would have outlived it's football replacement (FedEx Field), actually.
I'll be shocked if a PNC Park or AT&T Park don't last at least 60 years. The ones that are getting replaced are the ones that were obsolete within a couple years of opening. Plop this stadium basically anywhere but Florida or Arizona and it'd probably last another 15 years, but the lack of roof killed it and retractable roofs weren't truly figured out by the time The Ballpark in Arlington opened.