d4 Thieves can suck it

Can you spot the incompetent weakling?  The eyeliner should be a dead giveaway.

During my brief tenure in Holmesian D&D no one ever played a thief; partly because we thought they were bad guys and we all still wanted to be good guys at that point, partly because--shamefully--we had no idea how to roll percentile dice and, thus, could not figure out how to determine the success of thief abilities.  No, my first encounter with the thief class didn't happen until months later, after I had read The Hobbit and started playing D&D of the A variety.  As such, in my experience, thieves have always, always, always drawn their hit points from six-sided dice.  To this day, when I see these B/X retroblasters with d4 hitpointed thieves it makes me double over in agonizing cognitive dissonance.

Even if I accept that a lot of gamerfolk prefer Moldvanian D&D over all other forms, I still can't, in my mind, justify d4 thieves.  What exactly did they do to deserve such shoddy hit points?  They're only slightly better off than MUs in the armor category, with whom they share  hit dice, and yet they lack their magical potency.  Clerics, meanwhile, get better Hit dice, but also get to use bitchin' armor and spells along with combat acumen near to that of fighters.  The payoff for thieves is, ostensibly, a bunch of reusable abilities, but their chance of success with these is pretty atrocious.  And if you abide by Moldvay's overly stringent rule that, in the event of a failed "move silently" roll, the thief will be the only person in the vicinity who can't hear himself blunder across the dungeon floor, then you've got an absurdly impotent character class.  Why saddle them with such horrid hitpoints?  Why?