Who decided that England players based overseas could no longer play for their own country?
And, who decided that players in the English Championship are not eligible to play for their own country unless they join a Premiership club?

The answer, on both counts, are the clubs in the Prem cartel, and their protectionist, ring-fencing owners.
The fact that both demands have been rubber-stamped by the RFU tells us all we need to know about a union which, although it is responsible for all 1,400 member clubs under its aegis, is in thrall to just the 10 in the Premiership.
Restriction
In the past ...