The idea of having arcs that lasted for entire seasons, or even throughout the run of a show, was simply not considered a good move.
The thing that had worked, and worked very well, up until that point were episodic seasons of Trek.
Of course, it seems odd now that anyone would have had a problem with the idea of serialized stories on Star Trek, seeing as how powerful DS9 turned out to be, but it makes sense from a business standpoint.
Every now and then there’d be a two-part story that was resolved by the end of the following episode, but those stories were few and far between.