People suck, simple as that.
Mind you due to my name and luck I usually don't hover my pick in draft because people will ban it, however I was just so excited to play Ahri after I got the KDA Prestige skin that I picked her in the "declare your champion" round, and a pissy Midlaner who got autofilled Jungler banned her out of spite then picked a Midlaner champ a Jungle.
I could have stayed, and in a way I kinda wish I did just because I figured that person WANTED me to dodge so they didn't have to play Jungle and by leaving I gave them what they wanted - they won. However I was having a really sad day and that ban got to me, so I chose to leave and take the 5 minute penalty.
Now if you're talking about people who hold you hostage by not surrendering, all you have to do is look at these forums to see all the narcissistic tryhards who think surrendering should be removed just because they can typically do well in their solo lane - not caring about how the rest of the team is doing. They just wanna farm kills, talk about how great they are in all chat - repetitively typing "omg my back hurt" or "I can't carry this omg", and then crap on their team in team chat for losing the game.
Then you have the people who see it's a loss but actively want to "punish" the lane struggling the most and proclaim "Oh no, you picked that lane and now you want to surrender? No, suffer for being so bad!" (Literally, I've seen that typed in-game multiple times to people.)
So yeah, even when a game is an obvious loss you'll have people who want to hold you in the game for various childish or unrealistic reasons - that's just how people are. Should any of this be reportable or bannable? Well, the guy who banned my pick then picked a troll Jungle pick could have been reported if we got in the game and he either went mid with me or intentionally fed in-game - which was likely due to who he picked, but banning someone on champ select because of who they picked even if they seemingly try in-game is a road Riot isn't going to go down because it would set a standard of "you must pick A-Z for your role, and if you don't you can get banned" - which isn't really cool.
And then when it comes to banning the people who won't surrender, as annoying as that is I don't think it's anything someone should get reported or banned for, and banning them would be extreme af imo.
(Also, just an FYI in regards to what I said about surrendering.....I do understand a lot of people surrender too quickly, like within 10 min just because they died in a bad gank or something silly, and don't even try to come back from it. However there are also many many times where for whatever reason it's a VERY obvious loss, and people still won't surrender for the various reasons i mentioned.)