Size Availability Goes Down as “Quality” Goes Up?

I was looking to buy a few sweaters and was looking at Old Navy, Gap, and Banana Republic (which are all under one umbrella brand) when I noticed something interesting…

Old Navy offers up to XXXXL*

Gap offers up to XXXL*

Banana Republic offers up to XXL*

(*this is their largest size, but it’s not available for all clothing)

Do they not want certain people wearing their higher quality brand?

Is there a reasonable business or fashion explanation that I’m not aware of?

Or does it just boil down to exclusion?