Because you can point your subdomain to whatever support system provider you want on the DNS level and be done with it. No need for rules in the web server conf

Because you can point your subdomain to whatever support system provider you want on the DNS level and be done with it. No need for rules in the web server config. - Not all companies care about SEO for their support pages. - Having thousands of support pages can have negative SEO effects if you want only one single marketing page to be the top result. - Subdomains are probably not as hurtful as you think in some cases, but I’m no expert on subdomain SEO.