When the new Wembley opened the division of gate receipts changed.
Previously the FA and the two clubs got a third each after costs. That's how it had always been.
Since then, the two clubs share half of the gate receipts evenly after costs up to the semi finals. Then the FA take all the profits from the two semi finals and final.
It's a split that favours smaller clubs in earlier rounds and guarantees the FA a decent return for running the competition.
The reality is if this hadn't ever happened, Old Trafford would host one semifinal with Arsenal, Tottenham or West Ham possibly Liverpool hosting the other almost every year. Villa Park, Hillsborough etc are simply too small.
Yes Villa Park and Leicester's ground have been used for the Community Shield in recent years, but that money is for "charity"???? and not for commercial gain, so I'm sure different reasoning took place. It certainly wasn't travel considerations when City played Liverpool at Leicester a few years ago.