A main factor for paper count is simply group size. Let's assume a group size of 50 PhD students who take 3 years on average to graduate. If they write 3 papers each on average, which I would consider realistic, you quickly roughly reach the one paper per week range. I would consider it unusual to submit a too big fraction of the manuscripts to a single journal. But people make apparently strange decisions all the time, sometimes for good reasons.

A main factor for paper count is simply group size. Let's assume a group size of 50 PhD students who take 3 years on average to graduate. If they write 3 papers each on average, which I would consider realistic, you quickly roughly reach the one paper per week range. Certain more senior group members will quite often be an author on many/most papers.

I would consider it unusual to submit a too big fraction of the manuscripts to a single journal. But people make apparently strange decisions all the time, sometimes for good reasons.