Its kind of goes back to the issue with the CBA and the players having so much power (especially with agents like Paul involved). What can the 76ers or any other team really do if Ben decides he doesn't want to play somewhere regardless of how many years are left on his contract.
The Sixers (and all teams) can identify players that are likely to force their way out early, and trade them for top dollar before they become an issue, or never invest in them to begin with.
It's no secret this would happen with Simmons. He publicly said he wanted the Lakers to win the lottery so they could draft him.
Here's a post from me in 2016 loosely predicting this and saying I'd be leary of selecting Simmons because I knew this would happen.
There's a lot of trades the Sixers could have made over the last 4 years for Simmons. Sure you might not get a player(s) of equal skill, but it's a balancing act for teams, you can't just get the most skilled players, you have to balance skill, chemistry, longevity, with odds of winning.
If you want to get engaged to a girl, that all signs from the beginning pointed to her breaking off the relationship early and/or cheating on you, I won't feel that bad for you when she leaves you at the alter or divorces you after a couple of years to go be with someone else. The signs are there, you can take the gamble or get out of the relationship (or never enter into it to begin with).
Right away, what could the Sixers have traded the rights to Simmons for if they thought he's a flight risk? Probably Jaylen Brown + the C's Brooklyn pick next year? Maybe Ingram and next years 1st from the Lakers, or Ingram+Randle/Russell? Maybe the rights to Jamal Murray and a young Center picked in the 2nd round the previous year? After Simmons "rookie year" in '18, could the Sixers have traded him for the rights to Luka or Trae Young? In '19 could they have traded him for Morant (and kept Butler in the process)?
So they went all in on Simmons, and if a bum like me can see this problem coming 5 years ago, what's the Sixers excuse? (To be fair, maybe Kawhi doesn't hit the shot in '19 or Simmons doesn't get injured in '20 or a couple of calls go differently vs. Atlanta and the Sixers are polishing their championship trophies right now, it's a gamble).