Remind Me Again Why We Have a Debt Ceiling?

About a million political analysts have reminded us lately that it's crazy for the United States to even have a debt ceiling. No other country does, after all. And it doesn't make any sense: Congress incurs the debt when it passes a budget. Why bother with an entirely separate restriction on the level of debt? It's just goofy.

So here's my question: Since this is almost universally acknowledged, why do we have a debt ceiling law? Why wasn't it repealed long ago by a majority party tired of the opposition using it to score political points? My seat-of-the-pants guess is that repeal could be passed as part of the budget reconciliation process, which means you wouldn't even have to worry about a filibuster. You just need to control Congress and the presidency, and both parties have done that on a number of occasions over the past few decades.

So what keeps it around?