Sammo has been fat since the 1970s. They just keep him around because it is entertaining to see a fat fuck prance around with his man boobs flopping all over the place. As a fat fuck, Sammo served as a regular punching bag to real martial arts actors like Bruce Lee, Jackie Chan, Donnie Yen and any muscular AMDK villian.
In his fight against Donnie Yen in the "Ip Man 2" movie, they even made fun of him by having Donnie Yen squeeze his man boob real hard at 0:15 min. Fat fuck couldn't even last 15 seconds with Donnie without getting his nipples pinched.