I thought this hand was a bit primitive as well but instantaniously I came up with 2 thoughts. Despite their supreme technical knowlede maybe that was the best fully cabable working Arm (not just a hand) they could give him that would serve it'S purpose there is a 20 year gap almost.
Anakin Still had a job to do of protecting his newfound Love Padme from the evils that were after her especially with this newly escalated war. Maybe it was only a temporary Arm. He would be fitted with a nice one when he got some time to relax...