DPS players can sort of have fun on their own, whereas for a tank to have a blast (with the exception of Zarya and pre-execution Roadhog I'd say) it needs intense team coordination which is mostly non-existent on console matchmaking (can't speak for PC). If a Rein goes ham and starts swinging, he usually needs a healer on him and someone helping him with the damage, such as a Zarya. Mostly he has to stand there and progress forward switch his shield, same with Orisa. What about D.Va? You hold right click and let all the other stuff have fun. Sure you get some nice boops and maybe a huge ultimate, but mostly you're DMing. Winston is pretty dynamic but again, in my experience, heavily requires on the team following up.

Meanwhile Tracer and Genji can dart around the map, dancing around the enemies having a gay old time, McCree gets to use what is probably the most badass-feeling gun in the game, Sombra has a plethora of cool tricks and schemes she can get up to, deleting enemies as Widow feels awesome etc etc.

One thing I'd add is that the tank ultimate all feel awesome to use EXCEPT for Orisa's, which is clumsy and creates this silly looking bingo that you have to worry about protecting.