It's a meta-arch-aesthetic-principle decision on my part, not as the GM of DW but as like, a player of table-top games.
These principles are as follows:
1. Don't be a dick.
2. Make sure everyone is having fun.
3. Make sure it's the most fun possible.
4. Make sure you're also having fun.
Rolling the damage dice is fun for myself, but also fun for the players. Aesthetically, it makes it feel more like D&D. I randomize more than just the HP and DMG. I try and randomize pretty much everything. Also, the dice do decide somethings and like I their creative input as much as my own or those of the others at the table. If you wanna get all orthodox about it, you can disclaim decision making to the dice. I do it a lot.