Lucas said, (at the time anyway) he was going for an Arabian Nights fat sultan vibe with Jabba. Would you rather Jabba have looked like this guy? 😉
Yes. 😉
At least he was someone who could move and function like a crime boss.
That said; having him as someone who is never seen, just a plot point to keep our rogue hero on the run worked much better for two films. We never needed to see him. He worked perfectly as an unseen threat.