There's multiple things. Riders. Pork barrel legislation. Omnibus spending bills.

A single-subject amendment (that restricts the scope of a bill to one subject) has long had support, and in fact the majority of states have it in their own constitution. If there was a serious push, it could very well happen. But honestly it may be the lack of that that is the only reason any legislation can get passed at all, i mean look at the shitshow going on right now. Tacking the minimum wage onto the spending bill was realistically the only option available to pass it.