No games on older algos

Is there a reason why my older algos only have one or two games while newer ones are getting more? Is that in preparation for season 5 or is there a competition going on?

I’m pretty sure all algos only play each other once.
So your old algos play against every other algo that is about on your level (elo).
At some point it will have played against everyone and it proceeds to only play newly uploaded algos, as it played everyone else before.
Your new algos have a lot more options for oppoents, so they play against more people until they run out.
Correct me if I’m wrong, but I think that’s why.

I guess that makes sense but I don’t remember that happening before and since the season is about to end, I would expect people to edit and update their algos more often.

This is correct and is likely the main issue
Another factor is that new algos get a number of bonus games where they match very quickly so that they can move towards their correct rating.