Yes, D&D is a game that expects to be house ruled, and kitbashed, and flavored to taste. It's not a bespoke game. If you're evaluating it using the same criteria as a bespoke game, you're missing the point. As for people "long internalizing the idea", 5e has brought in a ton of new blood. How are players who've only played a few years (or even less than a year) long internalizing this concept? The simple answer is, they aren't. And the people you think have long internalized the idea haven't, they just recognize and accept D&D for the game it is, rather than what they think it ought to be.