Aircraft design is very intricate. Change the CG, break the whole system.

Fuel is often placed in wings because adding/burning fuel from your center of lift means your CG doesn't significantly change through a flight and you spend less on pumping fuel within the aircraft. With batteries, you are looking at a constant mass from the beginning of the flight to the end... so you can place it anywhere. Electric motors are orders of magnitude lighter than jet engines. Also, you don't need to pump electrons against gravity so placing all of that weight lower has handling/performance advantages.

By using an airframe shape that is well known, they are reducing risk and appealing to existing pilots. By building it from the ground-up, they are taking advantage of differences between the tech.

eg: all of that weight in the fuselage instead of the wings means that rolling is going to be much more nimble. Yaw might be affected as well, depending on the placement/moment of the batteries.

It may be too hard to do a good retrofit. If you basically have to tear the entire plane apart and rebuild and recertify it to put batteries in the right places, maybe the costs aren’t worth it for potential customers.

I know many planes use their wings as fuel tanks but given the weight of batteries maybe that doesn’t work.

I agree it’s interesting. Not a small undertaking.

I think an interesting aspect is that on normal aircraft fuel tanks have to be near the center of lift to maintain weight and balance as fuel is burned off. When using batteries, this is not really a concern, and I would think might lead to some more interesting designs. To be sure, if there is space in the wing, awesome - the batteries can now also be used as ballast though too if required.

Probably because they intend to sell aircraft, not electric motors.

Judging by the seats, perhaps making it as light as possible. Existing airframes are relatively light but let's be honest, they aren't trying to save 500g here and there when they have massive jet engines to get everything airborne.