MLB probably thinks the draft will go a bit longer in the future, eliminating the need for these UDFAs. In a 25 to 30 round draft there would be very few players that sign afterwards for a tiny amount of money, especially given the elimination of the short season A level.
The intent here is really to NOT sign marginal college talents and let somebody else develop them in independent leagues.
The 180-player limit probably means we will not sign too many more UDFAs. I doubt the number goes much beyond 10 and we are already at 5.