It's not hard to select the appropriate tactics and techniques based on situational context ...
if you train with some thought beforehand on what tactics and techniques are appropriate for a given situation and at least occasionally have training sessions to address different likely situations so you can practice switching your tactical mindset to whatever is appropriate for that scenario. If a practitioner never does that, they may fall into habitual behaviors which are inappropriate for the situation, whether that's MMA, a street assault, or something else entirely.
I occasionally set up exercises for my students which require them to do something different from normal sparring. Maybe they have to get past an "attacker" to reach an exit. Maybe they are on top of one opponent and have to react to a second opponent who comes to help the first. I've found that it's not uncommon for students who only used to applying their skills in only one context to get tunnel vision and stick to their normal game plan even when it doesn't fit the scenario.
On time in the "get past the attacker to the exit" game, almost all of the students ended up taking down the "attacker" and working for a submission instead of running to the exit as soon as they got the opportunity. The only student who followed instructions perfectly and didn't get tangled up on the ground was a brand new student who hadn't developed the sport habits yet.
In the case of the "second attacker" jumping to help his buddy on the bottom, I had one student stubbornly try to keep the first opponent pinned down while simultaneously trading punches with the second opponent.
This was after I had
just explained that the biggest advantage of knee mount is that it allows you to disengage quickly and retreat in just that sort of situation.
I don't think it's particularly
hard to switch tactics for the current situation. (At least not for me.) It's not even necessary to spend a huge amount of time drilling "street" scenarios. You just have to spend some time in advance thinking about it and getting occasional practice in switching gears so you can maintain a useful mental flexibility. It's been my experience that not everybody does that.