I use tmux a lot, but I don't use it for every session. To me, forcing me to use tmux to get scrollback is precisely violating the idea of 'one tool doing one thing'. You're forcing me to compose a Swiss army knife (tmux) into situations where all I need is a knife (a terminal that works well with the idioms of my environment).

I don't need tabs (I use i3wm), I don't need splits or session management (when I need that I use tmux). But I do often need to scroll back on a temporary session when I didn't plan for it in advance. I open a lot of terminals. They're never all going to be tmuxed.