producing something in a very high volume consistently is difficult.
my SO's father works in plastics manufacturing. they make tiny plastic housings used in cable connectors and tiny plastic balls for machine bearing seals.
both of these products have surprisingly high specification, and producing hundreds of thousands of them each day is a serious challenge.
It is, but probably for a different reason than you'd think. In automotive, the difficulty is not designing the car, but the facility to mass produce them. Elon found out the hard way. In his words: "it's trivial to design the machine, but it's hard to design the machine, that builds the machine". He is currently facing the same challenge with the production of the raptor engines for starship.
A million dollar low volume "hand made" car can be build by a small team, with relatively few resources. Operating a factory that produces thousands of affordable cars per day takes tens of thousands of people through the entire supply chain.