We know that Morbius has not only increased his intelligence by playing with the Krell technology, but without realizing it allowed his subconscious Id the access to a matter projecting machine with nearly unlimited power. This creates a monster, the "Monster from the Id". This has killed every other surviving member stranded on the planet on arrival because Morbius' ego did not want them to bring back that knowledge.
If we ignore the need to build up tension, Why does the monster first sabotage the ship and then (on the second visit) kill Chief Engineer Quinn instead of just annihilating the whole spaceship?
The only reason I could see personally was that Morbius' ego wanted other people to share what he found out about the Krell and therefore (subconsciously) did not want that the ship leave again.