BillyV81Because you will get so many other people complaining "I WANT TO PUT HIM INTO THIS EVO THAT EXPIRES BUT YOU WON'T LET ME, THE FSA EVOS ARE RUBBISH" or some such...
They show the rarity of cards post-evolution before you confirm for this very reason. People can make mistakes, own them.
If anything, the ONLY thing we should be complaining about is that you can't roll back or force-expire evolutions if a new chain suddenly becomes an option. Then again, tracking exactly what changes every time you do one would be so complicated and inevitably broken.