Why is personal shielding technology so rare in Star Wars? It seems only Durge and the Death Watch has them.
I am unsure about canon answers now, but in Legends canon it is revealed, on several occasions, that personal shields are actually dangerous to the user.
In Outbound Flight Kinman Doriana directly warns Commander Thrawn not to adapt personal shields from droidekas for use by his troops, as the radiation they produce "is harmful to living beings." In The Courtship of Princess Leia Isolder only uses a half-shield for a similar reason, limiting the damage to himself while protecting himself from an assassination attempt, and Luke Skywalker points out in Before the Storm that an enemy using a personal shield makes him more likely to kill them, as it is a lot harder to punch through a personal shield without killing the target than it is to render a person without one unconscious or immobile.
All of these would seem to indicate that personal shields are more trouble than they're worth. They'll protect the user from a a hand-blaster, but not a lightsaber or heavier calibre, and long-term use will destroy your body. Body armour seems to be a far safer alternative.
Wookieepedia covers the subject of personal shields. They're used in non-canon, particularly in video games (Dark Forces, Knights Of The Old Republic, Star Wars: The Old Republic MMO).
Personal shields were more prevalent in the Old Republic era. Wookieepedia speculates as weapon technology got better, shields became more expensive and required more power. The increased radiation made personal shields unhealthy for the user.