Ideally, you want the players to learn to approach a D&D fight in a more creative way than video game grinding and button-mashing. If they don't learn, though, that's as much your fault as theirs. You need to help keep them open to trying again, failing again, and putting their characters once more at risk.
One approach I've been thinking about recently is to make failure interesting. I've added this new system to my LotFP game:
INJURY AND DYING
At 0 HP, a player is unconscious. At -3 HP and every hit afterwards, roll on the following table. Cumulative -1 for every roll after the first during the same combat. At -10 HP you are for sure dead.
Lose a leg.
Lose an arm.
Lose a hand.
Lose d4 fingers.
Lose an eye.
Internal bleeding. Unable to move until healed.
Flesh wound. Looks worse than it is.
HEALINGPlayers heal 1 HP after a full night’s rest and 1d3 HP after a full day’s rest. Players with 0 or less HP must be the subject of a successful First Aid skill check (which can be made once per hour) to return to 1 HP, and will heal 1 HP for each full day of rest afterwards.
At my Sunday session two players were incapacitated, and they were both bummed out until I said the magic words: "Ok, now you have to roll an injury." Suddenly, failure was interesting. They were positively grinning at their lost eye and hideous scar.
Will this make them more likely to improve? I have no idea, though I like to imagine them looking down at their character sheet and thinking, "Ok, that's how I lost that eye, so..." But I do know that it made losing a fight way more fun.