The initial release of tmux was in 2007. The initial release of screen was in 1987. I assume they don't update as frequently because it's relatively stable.
(I mostly hear about this stuff because I still used screen and tons of people are like "why don't you tmux")
unbind C-b
set -g prefix C-a
bind-key C-a send-prefix
I use C-z FWIW.I had to still explicitly add `bind-key C-a previous-window` to emulate screen's `C-a a` to switch between last windows.
The default for `previous-window` is `prefix-p`. Run `tmux list-keys` to see all active bindings.