They didn't want to walk until level 40.
They didn't want to grind one dungeon 672 times for a .5 tier upgrade
They didn't want to buff every 5 minutes in a raid.
The list goes on, you've seen them all.
TL;DR: Everything that is gone from Vanilla/TBC/Wrath is due to player feedback. What you're suggesting has already been in place for years.