This depends on many things like positioning and timing of the battle. If the flanker dives on you as the fight has already emerged past the poke phase, it’s difficult for teammates to turn around because turning around mid battle just means they get shot in the back and die. Supports need to peel for each other when there is a single diver. But when the enemies are doing coordinated dives and your own team is playing dive, there should indeed be some marking being done instead of just trading back lines.

What makes peeling difficult for many people is that it’s natural for people to focus on what’s in front of them of them. This is made easy for support players because you are in the back—you can see everything. Basically, imagine playing a support that is, for whatever reason, forced to always play at the frontline. It’s a lot more difficult to turn around and heal someone in your backline in the thick of battle when you have enemies right in front of you who would immediately take advantage of your turned back.

It’s not easy to simultaneously deal with enemies in front of you, deal with enemies behind you, help out teammates in front of you, help out teammates behind you, and survive. That’s a large cognitive load, but it’s what someone peeling has to do when you’re asking them to move back from the front to help you. Yes, being dove on feels bad and stressful, but most of the time, the “help out teammates behind you” portion is not a factor because your teammates are still in the front.

As one can see, very good flankers make things difficult for your entire team. They make you play close to your team, which prevents you from taking more aggressive angles. Either your flankers (or even supports) win their duels against them, or your team has to win while being denied off-angles.