I don't know the NLA editor well, adding some people who do.

Probably an option like this should not be specific to keyboard operations (which is making some hardcoded assumptions about the keymap anyway). But rather something more general about how strip and track selection are synced.

Is there a reason why this must be an option?

I didn't want to change the existing functionality, which can be useful at times.
For example, you slide a bunch of strips around in the NLA, but have some others that were mouse-selected previously (and therefore their tracks are active), so you can tab into tweak mode to adjust only their curves without seeing *all* the selected strips curves, and without changing your selection again (to limit it to just those you wanted to tweak).

It seems convenient enough to have both and, when working on animations, I found I did actually go between the modes depending on what I was doing.