Fair point, but it’s a problem that plagues many religions where the decrees have been preserved but the reasoning lost or modified through interpretation. Who knows but maybe the list had an “etc.” in it that covers 9x9 but that 8x8 was the prevalent game of the times so it was called out explicitly. Or maybe 9x9 games took 10x the time as a 8x8 game, and no one could fathom spending days playing a 9x9 game. Or maybe it is just an arbitrary list. This is common with any law like the “right to bear arms” where new “arms” like rocket launchers were invented later. Unfortunately, the context appears lost.

I understood “negligence” to mean that playing games is likely to make you negligent of your spiritual or daily life. That’s still a common philosophy with parents chiding their kids for playing too many games and not spending enough time on school work, chores, etc.