Look, I get it. There are game rules in the D&D combat "board game" that can work themselves out to making retreat seem impossible if we treat the game as nothing but a board game.
PC Disengages from the monster and Moves away 30 feet. Monster Moves 30 feet and makes an Attack. PC either Disengages again and Moves 30 feet (after which Monster Moves 30' and Attacks again ad infinitum)... or PC Moves and uses action to Dash for 60 feet, but the monster thus gets to make an Attack of Opportunity. Then the monster Moves 60 feet themselves to become adjacent to the PC again, at which time again it's either Disengage and Move, or Move and Dash (both of which result in a monster attack at some point.)
If this was purely a mechanical video game with no narrative or story attached to either the PC or the monster... yeah, eventually the PC would die (or finally just turn around to face off against the monster and just fight.) But the thing is... this isn't a video game! There IS narrative and story. And you as the DM can think of any number of reasons why the monsters would not chase after the players, even if the mechanics of the game assured you as the DM that your monster could always win. Because that would be you metagaming as the DM-- knowing that mechanically the board game rules don't allow the PC to get away if you just have the monsters continually chase after them and attack when both are the same Speed.
So sure... if you want to say the game rules "suck" because they allow you to metagame and kill off the PCs no matter what they do? Fine. They suck. And if you want to see this loophole of "impossible mechanical retreat" closed in the new game? Sure! I'd be okay with that. Put it in the survey when the time is right, and maybe WotC will change the rule to close the loophole.
BUT... don't act as though the game is forcing you do anything, or forcing the players to do anything. Anything that happens is still due to your choices and the player's choices. And even if the game mechanical loop says a retreating PC will eventually be killed if you just keep chasing and pressing the attack... you do not need to do that. You have a choice not to. For whatever reason you can think of. And if retreat is something you want your players to occasionally choose... then ya just don't smack 'em in the face every time they do just because the "rules let you".