Brake caliper guide pins always stuck

The caliper guide pins with rubber sleeves is always stuck in position and troublesome to remove. Why can not it be straight metal shank? I removed the stuck pins by using sledgehammer and large screw driver and then re-lubricated the shank of the pins. However I do not know how long that will last until it will be stuck in position again(it should have slight freedom of movement).

why is the rubber sleeve so necessary and can I modify the rubber part so that I will not have it stuck in position or become hard to remove in the future? Your answer to my question will be gratefully appreciated. My other cars do not have this rubber sleeve features in the guide pin shanks and are NEVER hard to remove.