They do only if one wants balance at every level. That's not a priority for some; I'm fine with the long-term balance of warrior types being boss at low levels and mages becoming boss at high levels.
But that isn't actually balance. Like even in a long-term sense, it's not actually balance.
It's literally
not long-term balance, because
in the long term, things become more unbalanced than they were before.
Instead, it is, at absolute best, temporary middle-term balance: a range of levels where the exponential wizard is comparable to the linear fighter, rather than painfully behind or ridiculously ahead.
Long-term balance looks either like oscillation, where two things repeatedly crisscross one another and neither maintains a lead for long, or like convergence, where two things take different paths to reach the same result. Middle-term balance just means you have two things genuinely comparable
over some range, and anywhere else, anything goes.
It straight-up
is not balanced to make one thing objectively horrible for the early run, comparable for a little while, and then objectively the best thing after that. Because all that does is teach players, "Optimize the early run so you can get nigh-infinite power. Keep trying until you get it, because once you get it, you'll be too powerful to lose."
Keep in mind, I don't accept uniformity as balance. That's the lazy non-answer. True balance--asymmetrical balance, where different paths
really are different, but they're still comparable across a broad range of play--is a difficult but extremely rewarding target to reach. Many, many games have achieved it. D&D is only special by its all-too-frequent stubborn refusal to even
try to seek it.