What's with the exorbitant wait times on I-751 processing?

I'm wondering why there's such a long wait time to process these. Ultimately I imagine most folks will be filing N-400 before they receive their 10 year GC.

As someone who's conditional GC took ~6 months total from filing to card-in-hand, i'm curious as to why the renewal can take up to 2 years.

I understand that USCIS is understaffed and are probably inundated with cases, but is the I-751 just given low priority compared to other cases?