They aren't really slow or weak. Read the Wookieepedia article about them:
In summary, they can move in bursts of speed using the singular large muscle that acts as their "foot" (they are gastropods). Their skin makes them resistant to blaster fire, fire, and saber strikes. They are immune to many chemical and biological toxins, diseases, and poisons. They are immune to force mind tricks. Can see a wider range of the EM Spectrum than many creatures. They are indigestible by large predators. They can regenerate body parts. It is believed that some Hutts possess multiple brains. And they can live upwards of 1000 years.
I was hoping Hutt would be a playable race, but I see why they didn't that. I was also hoping you could play as a droid, but that didn't happen either.