[kemayo]

They could have raised the debt limit through reconciliation, but this shutdown isn't about the debt limit. This is literally the bill saying what the budget for the next year is, without which the government isn't allowed to spend any money (as opposed to not having any money to spend when it's the debt limit).

I think the reason they can't use reconciliation for this is that the budget has to include discretionary spending, and reconciliation is only allowed to be used for mandatory spending.