It’s not that confusing - Mervis’ value was (objectively)at its highest in 2022 when he hit .309 and smashed 40 bombs.
Instead of taking 30 days in September 2022 to see if he was a potential answer in 2023 (and possibly avoiding Mancini and Hosmer, who we are still paying) the Cubs waited, thus not knowing if he was an answer or not, until May 2023. He didn’t perform. The Cubs sent him down, and never called him back up the rest of 2023, and his stats have never been near what they were in 2022 or at the beginning of his time in 2023.
I am not saying Mervis was ever THE solution. But you could’ve actually received something of value for him in 2022/early 2023 in a trade. Now, he has no value.
You call up a guy in September and he hits .150 with 2 bombs, you typically put zero value into that when the season ends. Look at Rizzo with the Padres.
You call up a guy in May and he hits .150 with 2 bombs and then never call him back up because his numbers are never the same, your management hurts his value