I agree that owning a gTLD is not the same as registering a trademark, but I'm claiming that to a company it's the same as protecting their trademark. For the same reason that companies register their names on every new social networking website, even if they don't actively use it.

To give a slightly ridiculous example (just for fun), just as someone could make pickyourown.apple they could also register tim.apple and start an excellent phishing campaign.