Almost all of the smaller values of n are not valid curve values, so they were searching "harder" but for valid seeds. If you look at the generator output in [1], you'll see that:
reply1. Only a very small number of valid seeds were discarded when compared to the number of n values. It seems we don't yet know why valid seeds were discarded but the explanation of a buggy curve validity checker doesn't seem implausible to me.
2. Directly to your point, most of the prime192 and prime239 curves required larger n values to find a valid seed and they are both smaller and used an earlier timestamp.