My theory about this is simple. The lack of legends is an attempt to save money. If they can get the player base to accept less and less legends, then they don't have to pay for their likeness and it saves their bottom dollar. I think it is pretty obvious this year too.
There has been way more focus on active players and when they do release legends, they are part of a massive dump to get them out there (Moonshot).
This is coupled with the fact that many great legends are not in the game this year including
Fergie Jenkins
Ernie Banks
Mike Schmidt
Eric Davis
Frank Thomas
If you slowly pull back, then people might not notice.. and it saves money.
And if you replace Frank Thomas with Ben Zobrist.. it saves money
Just a theory though