The Spurs tanked for Duncan, fine, I'll give you that. But there were a lot of mitigating circumstances that year. The Cavs did not tank for Lebron. They were bad. Period. The Sixers don't tank - they are BAD, they would have been a lot better had they not had injuries to Simmons, Embiid and even Okafor.
You have one example, and that example was from 1996! 21 years ago. Up until maybe 2 years ago, nobody tanked, and those teams that tanked for the past couple years don't have much to show for it, including us, but we've only intentionally tanked for one year, MAYBE two.
Intentional tanking wasn't even a thing (even with the Spurs doing it in 1996) until the superteam concept started with Miami and now Golden State.