Because spam calls don't occur because you gave your number out, but because the spammers either farm your number from a "partner" or iterate through numbers.
That’s one class. Another class is if the number was in a credit application or marketing form, then got resold or data-breached.
I only put burner numbers on forms. They start to get called about 90 - 180 days later. Not all, but enough you don’t want to give your cell out.
I avoid giving it out wherever possible. Some forms require phone numbers, in which case I generally try to enter an obviously-incorrect number.