Because you're probably not spending enough time and money on the game. Either you have loads of time or loads of money. Best you've got both. Easy, right?

The  main reason is that Plarium is a for-profit business and wants a game that, as delicately and subconsciously as possible, coaxes people into spending money.

So I get that.

I don't think there's any reason for the upgrade process to be so slow, though.  They should either speed that up or get rid of it.  Nobody wants to watch that stupid charge bar for minutes on end.