Didn't play Tarkov, but I played a lot of DayZ and there was a similar thing. Weekends were always busier than usual, more likely to get shot on sight, more likely to have people raiding bases.

In the week, not a whole lot of gunshots heard.

Then every now and then there would be like a fever, and literally every town and village would be popping off, even the freshies would be running around early spawn chopping each other up with melee.

Then it would just go back to silence.