One of the reasons why 4E was able to keep going until level 30, and honestly could have kept going beyond that, is because it ignored the logic of how powerful PCs and their enemies were supposed to be. Instead of the only level 23 monsters being titans and ancient dragons, you could just fight level 23 bandits and skeletons, which meant you could keep using the same adventure formula at high levels that worked so well at low levels.
Your facts seem a bit skewed. You wouldn't face a bandit or skeleton at level 23 in 4e, it would be an astral reaver or a reanimated titan. This formula has existed and worked in every edition of D&D; at low levels you might fight bands of goblins whereas at high levels you are fighting bands of giants.
That said, most editions of D&D have placed the level cap at 20 (Basic D&D put it at 36, while 4e put it at 30). So, as others have said, there is a significant aspect of tradition.
I don't recall if 1e had them, but both 2e and 3e came out with expansion books that allowed you to exceed that cap. In 5e, epic boons appear intent to serve a similar purpose (also, while not official, I believe there are at least one or two epic level rules options on DMs Guild currently).
IMO, letting the numbers scale indefinitely would be counter to 5e's goal of bounded accuracy. If the numbers can get indefinitely big, then they cannot be said to be bounded.
Additionally, I believe the designers have stated that the majority of groups don't even make it to 20th level, so rules that would take you beyond this cap would have a very small target audience.
