I read somewhere that Palpatine purposely gave Vader a suit full of weaknesses (exposed buttons, vulnerability to electrocution etc.) so that he will be handicapped if he ever attempts to challenge his master (who after defeating the Jedi and becoming Emperor has no intention to die, probably ever). The Empire actually has access to technology to build much better suits than what Vader has to live in.
Considering that Vader, with his history of tinkering with technology when he was Anakin, should be well aware of his own weaknesses, why didn't he ever tweak with his suit or even change suits to remove those weaknesses?
Palpatine may not want Vader to ever remove those weaknesses, but it's not like he can openly express his desire to handicap Vader directly to him, especially if, for example, Vader gives the excuse of upgrading himself to better serve his Master. Such is the duplicity and politics of the Sith.