The thing is that the ones who steal are going to steal them anyway, even with the locks and sell them for parts. It won't really prevent theft but would only increase ewaste.
Are you sure? Seems like the market for spare parts would be saturated pretty quickly and the incentive to thieves would be reduced.
selling something for parts (which implies it will be used to repair other devices) does not sound ewaste-y so me
They don’t, though. As cited in the last discussion about this, the theft rate for Apple devices is much lower than ones which are usable by criminals.
Many parts of new devices are serial number locked or soldered (or both).
Makes the repairs hard though.