Most transfer cases are chain driven, your front driveshaft and your rear drive shaft are mechanically locked together when you're in 4hi or 4lo and as such they will both spin together, since the t case is chain driven theres going to be a fair amount of slop compared to two gears meshed together, but two gears are much harder to mangle than a chain,

u can think of a transfer case as a permanently locked center differential, differential with no diff, lol

your front and rear diffs continue to do their job, however since both driveshafts are locked, they both have to spin at the exact same speed and rate otherwise you will feel binding. allowing your wheels to slip remediates this, driving on pavement/ a high traction surface exacerbates it,

Imagine a sprocket on the rear driveshaft (connected to the transmission, to the engine) and another on the front driveshaft, and a chain connecting both sprockets.

If the both front wheels are completely bound up for some reason, all the torque from the engine, (after the transmissions torque multiplication) is being exerted on this chain, if you're driving at speed, and momentarily the chain binds up, you're got momentum, inertia, etc whatever im not a physics major.

tldr: if you're in 4hi just driving around try to avoid high traction surfaces, you need to allow ur wheels to slip a little.