Physics is not the problem. You can make the plane wider, longer, or taller.
It won’t sell. Airlines have realized that large planes are uneconomical because runways, engines, wings, loading, unloading, and flight times put 400 to 500 passengers at the cost-effective ceiling.
The main issue is health and safety. One of the rules is that you must be able to evacuate the plane within 90 seconds. These were tested with volunteers under test conditions. A wider plane would have a hard time getting all the passengers to the edge of the plane to get them off. So not wider.
Making them taller means more exits and longer slides. So you can get them off. However, most airports have only one height bridge. How would you get passengers to climb 4 floors without a 5-story bridge, which would mean splitting passengers into 5 floors of the terminal, which would require a complete redesign of the gate? Very expensive, so you have a plane that can hardly fly anywhere! So not higher.
It may be that the forces on a very long plane will put too much pressure on it.
