Not only is the "back bias" "helpful", it is necessary to prevent the transistors from conducting when they shouldn't, which could lead to a latch-up and catastrophic failure; hence the power sequencing requirements of these ICs.
(If you search online you'll find discussions such as https://electronics.stackexchange.com/questions/455745/why-w... where the accepted answer is close but not quite correct; -5 is substrate bias, 5 is the main supply, and 12 is applied to all the gates of the enhancement load transistors to open them. On the 8080, 12V was also used to drive the clocking circuitry, and this explains why the absolute maximum rating on all the pins --- and thus the gate oxide withstand voltage --- is 20V instead of the 6-7V typically seen for 5V devices.)
(If you search online you'll find discussions such as https://electronics.stackexchange.com/questions/455745/why-w... where the accepted answer is close but not quite correct; -5 is substrate bias, 5 is the main supply, and 12 is applied to all the gates of the enhancement load transistors to open them. On the 8080, 12V was also used to drive the clocking circuitry, and this explains why the absolute maximum rating on all the pins --- and thus the gate oxide withstand voltage --- is 20V instead of the 6-7V typically seen for 5V devices.)