That’s how it works. Certain gear slots will always roll your main stat if it doesn’t already have it. Random drop stats are mostly random but typically sway towards your class.

The upcoming patch is supposed to correct this, which will be nice.

Pretty much any weapon that doesn’t have mainstat isn’t worth rerolling currently as you’ll just roll main stat over and over trying to get something else (vuln/crit/etc).

Hopefully this improves soon.