That had a clear reason to be made, though: to add TLS 1.0 support to the console (which started being required by PSN, to avoid issues caused by its predecessor encryption schemes), (and to fix an obscure Japanese game in the meanwhile) - nothing else really changed, especially as far as obstructing modding wentNot very.
Think back to the PSP, 6.61 came out THREE YEARS after the prior firmware.