I dimly remember the reason for it not being recursive by default was it didn’t put local variables on the stack, and I guess /RECURSIVE (which I don’t remember) controlled that. Probably there was some SYSGEN parameter which limited stack size. There were people who would declare giant arrays as locals rather than putting them in named COMMON, so the user-friendly compiler default was to put them in a fixed PSECT because those same people would never be using recursion.