www. and just domain name have different number of pages crawled

[thu household]

I have set up 301 redirect on my example.com domain so that it points to www.example.com

when i do site:www.example.com I see 15000 pages in google result set
when i do site:example.com I see only 4000 pages in google result set

why would this happen..is there something wrong with my set up?

[iwannano1]

Google console (sitemap) has an option to display pages with www or w/o www. Login to sitemap and setup this option.