Blame the Gun Control Act of 1968 for this. It doesn't matter what two states are involved, at minimum the buyer has to go through a FFL. I do not know what additional paperwork the NJ resident has to go through, but a 4473 has to be filled out at minimum.
An NJ resident also needs an FOID. An out-of-state FFL may not know enough to ask for one (usually border state FFLs are in the know) but it's still required.
You do know that before the GCA, you used to be able to buy firearms via the mail and have them delivered to your door, like many do with a C&R, but there was no license. MD probably would still require a 77R to be done, but since 4473s would go away, it would be interesting. It would be nice, but it will never happen.