They know their software and update story sucks, so partnering with a company which promises to handle all that and they have an existing audience means they'll sell a lot more of that model.

My guess is that this is a great way for them to standout, fill a niche, and get tons of free advertisements in order to gain back some of their Android market share.

Motorola has effectively lost in the Android market and are on downward spiral into irrelevance (already there?), so they have to do something different.

Digital sovereignty. Europe is a big market and Motorola could gain traction this way

Sell devices who want to get out of the grip of US software monopolies. This is not unpopular in the rest of the world.