If you think people not connecting in 10-20% of games isn't a problem, then why is repeatedly nerfing or buffing champs that get played in less than 10% of games priority when it affects even smaller percentages of games?
Different teams.
In the last month or so, I've seen maybe 2 or 3 non/late-connects (one of them was me). Not connecting is different from afk or D/C [before someone tries to bring them up].
If I average 2 games per day, that would give me ~60 games. So that makes about 5% of my games. Since I don't have better statistics to work with, I can only work off that.
5% of games isn't much. You can make the one-million argument: if a million games are played each day, that means 50 000 are ruined. But it also means 950 000 are unaffected.
People design whole games in 5 years. Less time actually.
Sometimes it's easier to build things from scratch. Especially when you're dealing with someone else's crap. LoL wasn't originally designed to accommodate the phenomenon it is today. That's why so many clones are able to solve it's issues so much easier.
Should probably clarify, I'm not trying to "white knight" Riot. I have no idea what what their production pipeline or spaghetti code looks like. I'm just trying to point out that things are often more complicated that simply saying "do it".