"If he was able to leave the ramp, why couldn't the people leave the ramp as well?"
For the reason that Fox had a single chopper for him (that's my *assumption*) and/or a boat to ferry him across from the ramp to the Dome, but there wasn't helicopter or boat transport in place for hundreds or thousands of others...and there was 5 feet of water between them and the Dome.
And no room to bring food or water with them? And no way for them to find the authorities and tell them where they were? Instead they get on TV and shout like hysterical children when the authorities were obviously NOT watching TV, they were too busy trying to save lives.