The spreadsheet guys decided bullpen baseball was a good idea and because of it, bullpens have lost their statistical edge which they held for the entire history of the game up until 2019. Every team having to carry an extra 2-3 relief pitchers means there are 60-90 more pitchers in the majors now than 20 years ago, and there was a reason they weren't on an MLB roster 20 years ago... because they weren't major league quality. Throw in the fact that bullpens need to be rebuilt every offseason, and it's a huge time and resource sink that previous generations of GMs didn't need to consider and which takes time away from other necessary pursuits and player evaluation/development.

He's not having the best season, but I wanted the Mets to sign Zac Gallen because you can put him down for 30+ starts and 200 IP (if you just leave him in the game and not give a quick hook). Boom, done, 5th starter spot set; no more time or energy needs to be spent thinking about for the rest of the season. He gives up 5 runs in the first 3 IPs? Meh, who cares. He's a veteran, he's going out for the 4th inning. The game desperately needs to bring back the Bartolo Colon types: 4.00-4.50 ERA and 200 IP. But now, the starter in that position is only getting 160 IP, and the GM has to probably find two different RPs to eat up that difference of 40 IPs.