You're assuming that they don't allow this kind of tinkering internally. But they actually due, Heroes of the Storm and Hearthstone were both created as internal passion projects by staff, grew interest inside of the company, polished and released.

Blizzard does focus on quality and feel, and is very open about their willingness to push dates or cancel projects if it doesn't meet their quality standard. Titan didn't work as an MMO, and a lot of that work was reused in Overwatch.