NTAXS doesn't allow on-site registration for a few reasons, the main one being that we have an entry cap of 65. When you have 8 runs, you have to limit entries to get everything finished at a reasonable time. I'm sure there are other reasons that JRJ512 can explain, one of which is that NTAXS operates with a tiny crew compared to SCCA and ER (besides course workers, we had a starter who also setup run groups, one timing person, and one control/announcer person), so adding entries is difficult. We also set work assignments and run/work order in advance, balance the heats, etc.
Today we had 10 runs and finished by 2:15, with a 45 min lunch break. A big club w/ onsite registration can't feasibly do that.
Each club has strengths that make them good for the customers they serve. One of NTAXS' strengths is efficiency/simplicity.