I saw an article laying out the flight turnaround process. A cleaning crew boards, does their stuff, and left in just 18 minutes. Do you really think they’re cleaning the whole plane in that time? Of course not! They’re there to make it appear clean: picking up obvious trash, moving pillows and blankets.
I have no idea how often planes get an actual deep clean inside, but I would doubt it’s very often.
I always bring antibacterial wipes on planes to clean the seatbelt, armrest, headrest, tray table, TV, and above-seat air vent.
It may seem germaphobe-y but I’d rather know my seat is cleanish, than hoping that it’s clean.