But an N-1 is not as huge as an Imperial Shuttle, though.
Maybe it has to do with power consumption? I mean, for repulsor tech and craft the size of the N-1 and bigger, it probably requires a constant power supply to keep that tech running. Taking the size of a craft into account, it would probably kill any power sources for anything that’s big after a certain period of time. A thing to take into account for the N-1 is that they were probably power docking stations they were connected to in the hanger seen in Ep. 1, and that supplied a constant supply of power for the repulsor systems in them to keep their repulsor system constantly going. It could be possible that they went with landing gears for smaller craft because it’s cheaper for the in-universe craft builders to make landing gears to keep smaller craft’s power supplies from draining out quickly, while Speeder Bikes and Landspeeders don’t have as much of an issue because of their size. So, it’s probably easier on people to have landing gears than it is to have to constantly plug in a power supply to keep their ship from crashing to the ground while parked.
I’m just tossing out possibilities here.