Hindrances do not exist to penalize characters. They exist to define characters and how they connect to the stories of the setting. To quote the rule book (page 9)
Taking Hindrances not only helps you
define and roleplay your hero, but also gives
you additional points you can use to start
with additional attribute or skill points, Edges,
or even money for gear.
So ensure that you're approaching the issue of Hindrances from the perspective of defining the characters.
If a player never role plays a role playing hindrance then the Hindrance needs to be removed or replaced, because it no longer defines the character.
Removing a Hindrance is straightforward, but costly. (Page 54)
Permanently remove a Minor Hindrance,
or reduce a Major Hindrance to a Minor (if
possible). With the GM’s permission, and if
it makes sense, two Advances may be saved
up and spent to remove a Major Hindrance.
The player and GM should work out
how and when this happens. Perhaps the
shocking death of an ally triggers a change
in attitude, the hero puts real effort into
improving harmful behavior, or might even
seek professional help during downtime
But Hindrances are about defining the character, so it is probably more useful and interesting to exchange an ignored Hindrance for a more fitting Hindrance. If the Bloodthirsty fighter is now taking prisoners and turning in bounties then he is clearly no longer Bloodthirsty, but if he is also charging directly at the most imposing combatant on the hostile side then he matches the Arrogant hindrance and the GM can require him to do a one-for-one exchange.
It's noteworthy that every hindrance can be ignored. Possibly by everyone forgetting to apply the relevant rules, but more commonly by players choosing actions that avoid hindrances from being relevant. Heck, the Bad Eyes and Lame hindrances have mitigation written into them, and it's possible to go an entire campaign without ever breaking glasses or removing a prosthetic leg.
Still, there are always players that don't want to role play. Some days that's me, when I'm mentally exhausted. That can be fine, as long as they aren't making the game unfun for everyone playing.
If a player is only neglecting role play at rare and random intervals then they're probably also mentally or emotionally tired and just looking to relax without stress. Making them have to care, and increase their stress, is a jerk move that reduces fun.
If a player is consistently neglecting the role play of a Hindrance then that's a more serious concern. Possibly (and I've had this happen) the player isn't good at representing that particular Hindrance and needs to swap it out for something that will be interesting; the solution is to talk with them, learn this, and help them do it. However, the concern raised is that (extremely) rare category of player that refuses to role play their character's Hindrances.
I maintain that any solution needs to start with "talk to the player".
Sometimes the problem is poor communication; the player may think they are role playing and not being rewarded for it, or the player may not recognize the opportunities they've missed, or the player is role playing their idea of the Hindrance but it's completely different from the game master's idea. All three of those are communication problems that can be solved by talking things out.
While I haven't encountered it, it is entirely possible that a player isn't role playing because they don't want to have any drawbacks. ... Which makes their character really boring. I'd start with a conversation and figure out how to mention that "boring" fact. Beyond that, you're on your own - everyone is unique.
That very last category is the only reason to change the rules, and honestly I'd rather change the problematic player behavior. The danger of house rules is that they'll have unintended consequences. The danger of trying to get players to change behavior is that they'll leave my game ... and take their problems with them. Not ideal, but I'm okay with that risk.
Sometimes players just don't want to give into a Hindrance in the current situation. This is fine, but it can be fun for everyone if the GM holds up a Benny to tempt the player to go along with the Hindrance in that specific situation. Verbal reminders are optional.
I've been playing Savage Worlds regularly since 2008. I've been Game Master for approximately 150 unique Savage Worlds players. I'm also very active on the Official Pinnacle forums, where this question comes up frequently (about once per quarter).