I accidentally made an excess contribution to my HSA (or my employer or HSA custodian made a mistake, it's still not clear). I know what I need to do to correct it, but I'm curious, why is that allowed to happen in the first place?
The HSA custodian knows how much I've contributed at any given point in time, and they know what the IRS limit is (and that I was single). So why didn't they just prevent the excess contribution? That seems like it'd have been a lot simpler for everyone. Now I have to fill out a bunch of complicated paperwork, they have to process it and issue a corrected tax form, etc.
I've searched for reasons, but haven't found anything.