Bender had one of the worst scoring seasons ever. 35% from the field, 27% from 3, 36% from FT and really no offensive moves at all.
You want all your players to be capable scorers. Fultz has 2 way potential anyway, he has great defensive tools. It is not like you could just plug in Jackson and he would transform us into a suddenly good defensive team.
Look at Chriss in the first 2 months of the season, he was awful. The light didn't come on for him until February or so. Bender was injured for the majority of the season, which hurt his production. If the roles were reversed though and Chriss got hurt in January, would you be complaining about him? I doubt it because he's someone you liked right out of the gate, despite him showing very little early on. It takes playing time to develop and Chriss is a prime example of that.