Why did it take so long for keys with several accidentals to become common?

Question

(I am referring mostly to the common practice period.) Before the advent of well temperament in the 1700s, moving very far from C was not done often because of the mean temperament causing out of tune accidentals. However, disregarding composition exercises such as Bach's Well-Tempered Clavier, why did it take so long for distant keys to become common? Was it because of the relative difficulty of playing in them? Dvorak and the middle romanticists seem to be the first ones to use them regularly, although I don't know every single romantic piece so I might be wrong. But is there a reason other than the relative difficulty that distant keys took so long to become common place after the advent of well temperament?

Answer 1

You sort of answered your own question in the beginning, as to why deviations from the key the temperament centers around are avoided.

Though, if you mean "Why the key of C"? It's arbitrary. The pitch of the key of C major is only as absolute as the tuning of the instrument in its entirety (i.e. C = 260Hz, C = 220Hz, C = 285Hz, etc.). So with that in mind, why would composers of the time use seven sharps and write in the key of C# major, when they could just raise the tuning of the entire instrument by 15Hz?

Alternatively it's possible, I suppose, that romanticists were more concerned with contradicting musical tradition and being original. That could also account for "stranger/more difficult" keys.