It's not quite that simple. Owning a trademark doesn't automatically give you the right to seize the corresponding domain names. ICANN has a dispute resolution policy that sets out rules for how such situations are handled: https://www.icann.org/resources/pages/policy-2012-02-25-en
Basically, if someone snaps up the x.org domain, and can make a case that they have any legitimate purpose for it other than impersonating or extorting money from the X.org organization, they get to keep it.
Basically, if someone snaps up the x.org domain, and can make a case that they have any legitimate purpose for it other than impersonating or extorting money from the X.org organization, they get to keep it.