In the the "old days", I seem to remember that most plastic kits usually did include a pilot figure. Some, like those from Aurora, even had him molded right into his cockpit. I mean the real old days of the 1960's when plastic models were still marketed mainly as toys. Back then you wanted a pilot because how else was your P-51 Mustang going to look cool hanging from your bedroom ceiling shooiting a Zero with cotton balls stuck on it to represent MG hits?
When plastic models improved in quality and modellers got older (not sure which was the chicken and which was the egg), we wanted detailed cockpits (which was a natural place to add detail). If you stuck a pilot in his seat (no matter how well painted he is) people couldn't see the hours of work you put into the teeny throttle down by his left knee or his rudder pedals. So, kit makers generally stopped providing pilots, although occasionally you could find kits with really nice multiple piece pilots that could be realistically posed. Now, it seems pilots are generally absent, except as standing figures to be placed next to aircraft in a mini-diorama. I recently saw a kit of a Soviet Pe-8 (Zveda, I think) that was Stalin's personal aircraft with tiny figures of Zhukov, Molotov, and the Great Leader himself you can pose by the doorway. Now that's cool.