I am fairly confident that this is not the reason for the file descriptor limit, especially since select was superseded over 3 decades ago by by poll (1987, pic

I am fairly confident that this is not the reason for the file descriptor limit, especially since select was superseded over 3 decades ago by by poll (1987, picked up by Linux in 1997), which in turn is superseded locally by kqueue. Use of select in modern times is a bug. ulimits are quotas that disallow excessive resource consumption by an application, not bug shields.