"pulling the return address off the stack" is pretty typical in nes 6502, see it a lot for handling stuff like jump tables or similar "data stored after call" setups.

this game instead has a subroutine that just grabs the stack pointer and reads from the return address two levels in.

i'm not sure why they did this, but i'm similarly not sure why they apparently copied and pasted the same "switch to these two banks" bit of code 18 times. but who knows