I notice in the marketplace many people are selling off their aftermarket parts, saying they are going back to stock.
Wondering why? Does it have to do with resale?

 

I'd say generally resale. You never get the money back that you put in with mods if you sell them on the car.

 

Yep. Aftermarket parts add little to no value (and sometimes negative value) on a used car for sale. My rule of thumb is that you can get ~50% of list for used parts (some more, some less - i.e. my euro parcel shelf is currently worth more than what I paid for it due to lack of availability.)