There's actual good reason for that. the X Formally Known As Twitter company has a content weighting system that punishes external links, regardless where the link is pointed to. So apparently Mr. Soham did the smartest thing to give that post the best chance to spread.
BTW, the X Formally Known As Twitter company is not the only one who conduced the world to this, all big names do link restriction. Look what we've become, such nice world :)