I understand that logic, even though I disagree.
There's still plenty of room to get more money from people, besides the normal subscription.
I'd like to remind you the blizzard store pets,the TCG mounts etc, even the cosmetic bullshit they just recently added.
In my opinion devs decide to go f2p coz it makes them sufficient money for the mediocre games they chose to make. It's like they know their game is average and don't have the balls to take the risk of adding a monthly subscription to it.
I mean even if there was a monthly fee required, they could still sell all the non p2win items they intend to sell. Blizzard does it.
The reason they chose not to ask for a sub, is because the game will fade into obsolescence eventually.