It certainly is a common request. Only logic I can see behind them doing nothing for years and years now is the fact that EMC bought them; maybe they want people to waste tons of disk space so they buy more storage. We decided to task one of our staff with zeroing and live migrating forward and back bloated VM's every few months and it never fails to recover several terabytes of wasted space on our arrays.
That is one of the few nice things about the horrendous new 5.5 interface; on the Home -> vCenter -> Virtual Machines screen, it gives you a chart of all of your machines and two of the columns are provisioned space and used space, and you can sort it by them. Makes it very easy to spot the bloated guests to target for cleanup.