That's just the taper doing it's job,Could be. On the right side, the footrest doesn't move even with the nut undone.
Hasn't been taken off much like the left side.
I'll compare the two sides to see if the taper is different.
The very outside of the tubes sometime nip up on the stud, Need a tap with a soft hammer,
To get off.
I have seen the tubes made out of steel, But a lot are alloy.