It's definitely that in part, I would have to agree with you. This generation of gamer grew up with the relatively easy ability to pirate games instead of pay for them and steam sales on PC. So there is some resistance to paying for it even if it's not outspoken. My own personal reasoning (now that paying for a game isn't saving weeks of allowance) relies more on resistance to change on the way things have always been, with a bit of skepticism on the way they are monetizing the mods with the split amount.
After playing multiple games by Bethesda that have been relatively unpolished compared to what the modding community has done, I see the move as a cash grab by Bethesda in releasing a game and cashing in on people who just want the game to be more playable by selling the mods to other players as free generated DLC content. I understand that the modders have a lot of a headstart on the work as well, given to them by Bethesda, which is why I wouldn't support modders selling mods on their own. I think the free + donate model has worked very successfully in the past in both motivating and (I assume, but can't be sure in generalizations) compensation.
My last note on the issue is that at the very least this move should not be implemented on a fully developed modding ecosystem where the mods have already intertwined to a degree that this causes a single person decisions to need to be made by multiple mod developers. With mods using other mods, it would be acceptable to have to buy the used mod if that was a design decision by the original modder, but that information was not present as the ecosystem developed and I think it introduces a great deal of harm. As a source I cite all of the trauma that Nexus experienced in the wake of this system being released.
