Because unlike most large workplaces that inhibit innovation and productivity and infantilize staff with an “anything not specifically permitted is prohibited” rule which also creates continuous work for a review and approval bureaucracy and guarantees that toolsets are outdated and improvements difficult to discover, Google apparently has an “everything not specifically prohibited is allowed” policy.
There's a third "use at your own risk" option between the two extremes. Sure, install your favorite terminal emulator, but if it steals your production credentials you may get fired...
