I think it's just not worth it. Gates would have to be redone at huge expense with aerobridges on either side, and the technical challenge of putting the bridge over or around the wing somehow would be formidable and expensive. Airports would be loathe to eat the cost. And unless you very tightly controlled the passenger load order and which side they were on etc, there'd just be chaos on board anyway with people colliding after loading from the wrong door.
I think the fact is that even though it annoys us as passengers if it takes 10 minutes to get off the plane, it doesn't make all that much difference to the turnaround time. There's still fuel onload, baggage and cargo off/onload, catering (which uses the back doors currently), waste materials offload, technical checks.. there's a certain irreducible amount of time it will always take, which increases with the plane size.
The fastest I've ever seen a flight turned around was about ~15 minutes (a late 737 trying to get away before a storm hit in Sydney), skipping catering, cleaning and my bag. I've heard SouthWest aims for about 25 minutes, but they had to get rid of assigned seating and be pretty strict with carry-on luggage to achieve that. That seems like the most optimised anyone's going to be able to do, and that's exclusively 737s.
I've heard of refuelling being done with 2 trucks though. It can take 2 hours to fuel a 380 going its maximum range. If a plane was an hour late and they needed to turn it around fast to meet a curfew, that's something they can do. Wouldn't be worth it with narrowbodies which can be done in 15 minutes.