Di2 is mostly popular among the performance cycling set who likes to go fast. The ~5% drivetrain power loss you'd get from a dynamo isn't attractive in that market. Also, Di2 requires charging every couple of months. It just isn't worth it.

I have seen some randonneuring bikes with a dynamo with USB charging for topping up the bike computer and the like. Commuting and utility bikes tend to just use the dynamo for lights.

That’s a market that’s entirely foreign to me, I use my bicycle entirely for commuting, buying groceries, etc so I’ve got a hub dynamo powering the lights.

I’m honestly surprised that there’s no super-low-power hub dynamo for this segment, but if it’s all people using bicycles for planned trips, they can take charging into account when planning trips.