From an editorial in today’s New York Times :
Senator Jeff Sessions of Alabama blocked the extension of the G.S.P. [Generalized System of trade Preferences] altogether because he couldn’t get sleeping bags removed from the program. He was acting on behalf of Exxel Outdoors, a sleeping-bag maker from Haleyville, Ala., that competes against sleeping bags imported duty-free from Bangladesh by CellCorp of Bowling Green, Ky. The Republican leader, Mitch McConnell of Kentucky, was pushing to pass the G.S.P. in its entirety, so Mr. Sessions put a hold on the bill.
Public-choice theory  might not explain everything that happens in politics, but it explains a great deal – I would say most – of what goes on in legislatures.