They don't allow direct credit gifts because they would lose the rake in Challenges. The rake is justified because it guarantees the loser pays.
Typical backward thinking of the WGT brain trust.
1) Some players can't play challenges due to "laws" of wherever they are;
2) Randoms can get around this by playing for pro-shop "gifts" although, there is no recourse to the winner if the loser doesn't pay off
3) Challenges mainly appeal to random trying to hustle other randoms.
4) Friends can get around that by just playing for pro-shop "gifts" No sense in 2 friends playing match play challenge for credits instead of a sleeve balls.
5) WGT still gets all the money from said "gifts" they only "lose" the rake.