Usually these marketing sites are running a CMS (this one looks like Drupal) which is owned and operated by either an internal team who report to the CIO / IT department (vs the Product/Engineering group) or a totally external third-party marketing firm.
As long as the "real" product uses different subdomains, certificates, proper HSTS, cross-origin protection, and secure cookies (a tall order, yes, but something that would be an issue no matter what the marketing site is doing), security issues in the "marketing" site aren't as bad. Of course a marketing site takeover is still worrying, as it's a prime entry point for spearphishing and horizontal movement through social engineering, but these usually aren't the same engineers or security team at all.