There's no other logical reason. Why would you care about someone's past sex life? There is nothing inherently wrong with enjoying sex and having multiple sex partners. You could bring up stds but even that has nothing to do with the amount of sexual partners and more to do with use of protection. And then you could say that high n count people are more likely to cheat and even that makes no sense because people are generally single while having different sex partners. If men want a asexual women then yeah sure that makes sense that you'd want a low n count partner because that points to asexuality.

So it comes down to jealousy. Were her past partners better in bed? Did they have a bigger dicks? etc etc. Which i think is classic projection because women dont compare their sex partners- men do.