Huh, in Tokyo and Osaka I didn’t encounter a 7-11 without self checkout as an option. The smaller convenience stores sure, but not 7-11. China is much more aggressive in this regard though.
They might have one person ready, but the amount of volume they do means that the kiosks aren’t really that optional, most people are using them or they would be waiting awhile for human help (and most people use them so the manned check is pretty clear most of the time for those that need it).