I don't see the correlation between those and making new heroes free. Maybe as a way to douse the community flames.
I think it's simply because people want to play the new content. While some cave and buy the battlepass, it doesn't offset the losses of the grind and paywall that stops people from coming back and investing to begin with.
It's a good change for sure, but the cynic in me can't help but think they're doing this solely because they believe it'll make them more money this way.