Cost has a lot to do with that. Compare 101 Dalmatians ('61) with Snow White ('37) and the newer one looks cheaper because it's cheaply made - copy machine tech instead of artists for part of the process.
The real problem is that Disney movies boom or bust. The insane successes (Snow White, Dumbo) were offset by busts (Cinderella, Bambi). Ironically, even though we remember these are huge successes now, Bambi was released in the middle of WW2 when the international market was cut off, and Cinderella was a box office bomb.
Disney still has this problem, which is why the death spiral of a Disney CEO is always when they start greenlighting sequel after sequel.
Is that really so? Wikipedia says it was the 5th highest grossing film of 1950. [0] Quoting the same: "Walt Disney Studios' animated film Cinderella debuts. The film is the most successful the studio has made since Dumbo, and saves the studio from four million dollars in debt."
My bad.