Bacon Bits
Legend
Yeah, as I said, there's actually no specific fundamental underlying principle here. I just remember the day I cracked open a PHB1 in 2008, and as soon as I grokked what they had done, THE very first thought in my head was "this isn't scalable." I mean, I honestly don't even comprehend how anyone in WotC thought it WAS and why they made such a blazingly obviously bad strategic decision. I mean, it MIGHT almost work with 5e spell lists (as it did with AD&D ones) simply due to the fact that so very little additional material is planned, the lists were intended to BE complete as written. 4e was never intended to be so, it was designed, clearly and undoubtedly with near-infinite expansion as a central tenet.
I thought it was pretty straightforward how WotC expected it to scale. Digitally, with the required labor of evaluation of all the content expected to be magnified by the power of the Internet. The same way that video games with a similar quantity of choices scale. Since the devs were able to issue power level errata (i.e., nerfs) then anything viewed as a real problem would just be altered. (Like, there's a reason that the last 4e errata documents I still have are themselves long enough to be a hardback book.)
The central conceit was that they expected the Character Builder to be a uniform tool to manage all the content of the game. And, until it was abandoned, it actually did a pretty good job of that. When you made a character it presented you with the options actually available to you. If you were the type of player who loved to fiddle around and built characters, this was an amazing amount of fun. I probably created a two dozen characters for each character I actually played. 4e's character building minigame was a lot of fun.
IMO, one of the bigger nails in the coffin to WotC's business model for 4e was the ending of support for the Character Builder (never mind never getting it to work outside the Windows platform). Without that, the amount of content between class powers, alternate class features, races, paragon paths, epic destinies, magic items, and feats plus all the errata is very clearly totally and completely unmanageable. I'm sure there are tables that managed to play the game completely on paper with every book printed, but there are people who play Phoenix Command, too.