Who cares? That right there tells me that the career of a player doesn't matter but only the drama that can be fed off of the player.
If you want that, then don't make everyone deliberate trash talkers for the sheer sake of drama. Not everyone needs to ooze swagger and cockiness only to have their words haunt their careers by fans who are only out to hit a nerve.
There's players all over competitive games that can tolerate that stuff. Particularly in the FGC: Marn - no matter where, when, and how far he gets which usually isn't much - is one of them. Will trash talk and pop off any chance he gets but it's expected of him by now just as it is with DL.
With League, you really don't get that same feeling unless you're worthy enough in the light of fans. Dardoch and Gilius are two very common with a rep of talking the talk only to have their communities walk them off the stage. At least in Dardoch's case he found his way back when he eventually shut up enough.
Hell even staged trash talk leaves a dramatic hit on the community. Why do you think it's never done anymore? Trash talk is normally something held onto for days, maybe a few weeks; not years! The scene's too small for one statement to be drowned out. And one's career is too limited from how easy a hothead can get axed for their own words. And for what: drama? Everything becomes a headline which becomes a meme which is never let go until proven irrelevant.
So before you say other sports can do it so this can, perhaps think about how much League pros look towards and even fear their own community and fanbase leading to how their words are so restricted.