It’s not the papers per se that get you tenure — it’s the grants you bring in, and you can only get those by going through funding agencies, who are the ones that care about your publications. The grant process is like this: you write a proposal that says “I want to do this. Here’s how it will work. I’ve published these papers to support my idea. Now give me $x million dollars”. That pitch only works if there is a significant publication record to back it up.

That’s why there’s a monoculture — everyone is going through the same agencies: nsf, darpa, and a handful of other government/institutional funding sources. If you are bringing in 10s of millions of dollars worth of funding into the university with only a handful of papers, you’re going to still have a lot of support for your tenure. The flip side is that you can publish all day every day, but if you’re not bringing in grants you’re not getting tenure.