I think it’s that he has no position, doesn’t get on base particularly well, doesn’t have a body that ages well, and has been injury prone. I think trading Burger was a perfectly fine thing to do when your team needed to improve on defense and get away from RH free swingers. You can argue the return, but the jury is still very much out on Eder.
I get Burger was an easy guy to root for him. I like(d) him too. But worst trade in franchise history? My lord, what a take!