I think it's probably just a coincidence, but it could also be a combination of many factors, such as player fatigue and one team's increased intensity. It could also be that one team is defending, not wanting to win and simply wanting to waste time, while the other team sees a chance to equalize and throws everything they have into it. Incidentally, at the last World Cup, I really noticed a lot of goals in the final minutes, but I haven't looked at the statistics for other leagues. Perhaps the same thing is happening there, which would certainly indicate a change in processes and strategies in football.
It might have something to do with the strategies of both teams, but I don't think player fatigue can be a reason for it, because if that's the case, then players from both sides should face the same problem, but if one side is still active while the other side is not, it doesn't indicate that it's because the players from one side are tired while the other team is still going well, because obviously, even if a team has some substitutes, they can't do that with all their players on the field, and both sides can do the same number of substitutions in a match.
I do agree with you on the strategy thing though. It is possible that maybe some teams play more defensively while the other team goes on attack mode, and in that case, the team trying to defend loses and attacking team scores. And, even if both sides start attacking more on the last few minutes, it is possible that one of them or even both succeed in scoring, so they might be trying to defend in the whole game, and then start attacking towards the end.