Doubt about 301 domain expired redirect SEO

Hi all,

I have a doubt regarding a redirect 301 from a expired domain to main domain.

Recently, I've catched an expired domain with backlinks from 98 different domains, accordingly with Semrush stats.

So, I did a 301 redirect to my main domain in order to get this backlinks.

However, after two months, my main domain only contains backlinks from 21 domains checking the same tool (Semrush).

My question is, why I did not get the 98 domains backlinks after targeting the 301 redirect?