Martin Maldonado
Martin Maldonado is a tough case where an organization's loyalty to a player and his previous contributions clouded the reality of his decline. Maldonado was never a good hitter. The only season he ever posted a better than average wRC+ was 2020 and his slash line was still just .215/.350/.378 which isn't exactly awe inspiring. However, Maldonado was an excellent defender who managed the pitching staff well, so he was serving the role as a bridge to the future for Houston at catcher nicely.
The problem, of course, is that wasn't a bridge for Houston....he just turned into their guy who got the bulk of the starts at catcher. His defensive numbers weren't as strong as they were during his time with the Brewers and Angels and his offensive game got more and more abysmal. Fast forward to this year and Maldonado has not only been terrible at the plate with a 50 wRC+ which is impressively bad, but his defense has left him as well. Houston just hung on too long to a guy with very limited upside here.
Forrest Whitley
Pitching prospects are among the most likely types of players to bite you in this sort of way and Forrest Whitley is a classic example. There was a time not that long ago where Whitley was considered one of the absolute best pitching prospects in all of baseball. The Astros picked him 17th overall in the 2016 draft and very quickly climbing the minor league ladder thanks to having a ton of above average to plus pitches when he is on. All he needed to do is take that one last step with his commanand he had a chance to be a front of the rotation starter in the big leagues.
Unfortunately, that did not happen. First, Whitley got hit with a suspension for violating MLB's drug prevention and treatment policy which cost him 50 games. Then there were the injuries and there were not a small amount of them as he had some kind of injury issue every single season leading up to having Tommy John surgery in 2021. Instead of moving him at the peak of his value, Whitley's value has cratered to the point where if he makes it to the majors at all, it is likely going to be as a bullpen arm as he hasn't shown the durability or consistency to cut it as a starter.