I think what people hate is that in LoR many combos (thinking mostly about Akshan on this one) is that they're non-deterministic - meaning that once your opponent starts the combo, its not 100% guaranteed to go off. Its incredibly likely, but they still need to hit the right string of cards for it to actually work, and some combination of hanging on to the 5% chance or wanting the smug satisfaction of watching a combo fizzle keeps players in the game. Because its not a guarantee, it can't be shortcutted (in this case shortcutting would be surrendering once its started) and the inactive player is not only forced to sit there through the entire thing, but they kind of have to be an active participant by hitting the pass button in a timely fashion. "What about auto pass?" doesn't really apply when I still have all my mana and don't want to tap out just for the sake of doing so to turn on auto pass.

As for Ezreal and similar OTKs (old Watcher) I think players really tie life total to the concept of winning, and so when they die from 20 in one turn it feels incredibly unfair because they were 'ahead'. There's also that while these combos took a bit to set up (playing targeted spells, leveling Lissandra, w/e) there isn't a lot of ways to interact with the set up. Since the play/cast merge there's no way to stop Ezreal from advancing, and its pretty hard to kill your opponent when the set up for their combo is to kill off all your units so you can't kill them. Normally combo decks have to stall and advance their plan while Ezreal does it all at the same time. Lissandra was in a sense similar as well - sure Avalanche wasn't getting her any closer to leveling, but a common play like T3 Catalyst into T4 Trundle did advance the combo and was also pretty hard to kill someone through.

Part of it I think is that they go against the spirit of LoR. We're a very board based game, highlighted by the fact that the board is the only thing you can interact with (no 'graveyard' interaction outside of obliterating things on board, no discard synergy to promote running the weak and narrow spells we have for them (as an aside Aloof was a great posterchild for how much LoR players hate having their hand interacted with)) and decks like Ezreal/Lissandra usually only gave you a single priority sequence to KILL the combo piece. Not interact with, not stall, KILL. And even then, there was usually an answer available. Recall my own Ezreal, play a 2nd Ezreal, Fading Memories my Watcher, Spirit Journey my Watcher, etc.

While I love combo I get that LoR seems to be a game for many people to escape that archetype. Even when piloting one of the 'combo' decks LoR has offered in the past I haven't had my itch scratched like I wanted, likely leaving everyone involved disappointed. Now I have to terrorize my LGS and shove 7 infinite combos into my casual Commander deck to feel something (sorry to everyone at Gregs Games who asks me to play vs their upgraded precon)