OH BOY A BASHING THREAD!
Anyways,
The Long Answer
repainted rides, theming and areas apparently does not bring in any guests for a profit company. Unless it's part of a re-theme or directly next door a major new ride, it will be ignored unless it breaches safety regulations (sadly often resulting in just removal instead of replacement).
The short answer
They don't really care about presentation. Just profit.
There are parks out there though which do take some care for presentation though. Notably Paultons, Blackpool & to a lesser extent Drayton.
(awaits criticism from a fanboy).