The thing is Hamster, Airplane industry is a very limited industry. Large commercial jet market is only about 1000-1500 airplanes per year, split into two. Orders fluctuates every year. Boeing may never be able to sustain 1000 orders-year like last year. Because of this fluctuation, Boeing cannot simply increase its capacity to respond the market.
Say, this year Boeing receive 500 737 orders, and they increase their factory output to 500 planes per year, to cope with the demand. What happen next year when it can only sell 100 737s. Are you suggesting Boeing to cut the capacity? It's gonna be very expensive for them to do so.
Car market is different. Since the market is so large, they can more accurately predict how much sales they're going to make for a given year, and the uncertainty will likely to even out. Even then, GM
and Ford sometimes overestimate the market and produce too many car, and hurt their bottom line. Just like in the recent years.