The thing is, people don't int or troll all the time, they just do it when they feel like it (they don't get the role they want, they don't get the champ they want, the team comp isn't what they want to play in). It's not necessarily a pattern of behavior, it might not happen all the time, but the damage it causes amounts to 4x(game time) + whatever negativity between players arises. Whereas the damage that a flamer causes is exactly how long you decide not to mute them.
The rationale that people deserve to be banned because of chat used to hold up when you needed to type "mia" or "rb", "bb", etc, and chat was important to playing well as a team. but the ping system is so good now (MIA, warded, help, on my way, back off, look at this) that it isn't necessary to even have chat enabled. I would absolutely play with chat disabled in ranked because all of the information I need to perform well in ranked is communicated through pings and having game awareness. Inting and trolling are categorically worse than flaming because there is no way to escape it, you have to play it out. But there's no option, you have to type a command to get rid of it that I completely forget about until someone starts tilting at someone else.
That's a shitty way to have to spend time that you set aside to have fun. It's also shitty that calling someone out or flaming them for being like that is treated as worse than actually ruining the game for others. Like, this is the only online game I've ever played where being a complete jackass and ruining it for four other people is possible in such a way that a troll can provoke 4 otherwise innocent players to break the ridiculously militant chat rules and get banned while not getting punished or having their behavior reprimanded in any way (in fact, they are encouraged because it gets the results they want). That's an objectively terrible system.