What are the obstacles to education reform in the Harry Potter universe?

Kalinara over at Pretty, Fizzy Paradise raises a point I’ve seen before:

But they take the traits MOST likely to result in evil wizardry (ambition and cunning) and shove ALL of those people together into one House. Doesn't that seem like a recipe for disaster?…

It's like...prison really. In which some poor kid gets thrown in for drug possession or something and comes out with all this knowledge and ability to commit much bigger crimes. Only, you know. The wizard equivalent. You go in a little brat, and come out a Nazi.

And really, isolating most of the really ambitious people together in a system that promotes solidarity-in-ones-group and competition-with-others over anything else, just makes for another mess.

I quite agree.  However, I wouldn’t necessarily just trace this idiocy to bad writing.  This sort of phenomenon can happen in real life, see the prisons example.  The question is, why is it allowed to persist?

Here’s some causes I could see:

1. Follow the money: Certain influential people find it desirable.  The schools are run by the Ministry of Magic, but that doesn’t mean that they don’t have endowed chairs or powerful parent associations.  It could well be that either Salazar Slytherin himself, parents, or alumni  based their financial support (in gold or in magic items) on the maintenance of Slytherin in its present form.  Given the close affiliation of the Houses to sporting events, it wouldn’t surprise me at all if much of the fundraising came in through the houses and not to the school directly.  Slytherin grads seem to be the richest of the bunch and the first Voldemort uprising wouldn’t have automatically broken this system as many supporters made it through with their fortunes intact.
2. Slytherin students as a public goods problem: Perhaps the other houses prefer to not deal with Slytherin students.  Some of them are ambitious and clever but a good number of others seem to be toady material.  Abolishing or reformulating Slytherin would mean other houses taking students they might otherwise prefer to avoid.  Any one house wouldn’t want to take the bulk of the more questionable students thus shaking up the system would require coordination of multiple actors and not just one brave reformer.
3. Legacy systems: The sorting hat apparently includes blood purity as a factor in placing students.  If you think upgrading a bureaucracies IT systems is hard, imagine what it would be like if that system really was created by an arcane ritual that was likely only known to its creator.  I’d also say that the methods of education at Hogwarts are on the whole terrible, a good cross-house team building class would go a long way to remedying the problem but given that the school doesn’t even have a computer lab I doubt we’ll be seeing that sort of thing any time soon.

On the whole, I tend to think following the money is the most logical explanation.  Real reform seems unlikely because the wizarding world is in many ways a larger reflection of Slytherin house.  The Prime Minister seems to have less power than the Minister of Magic who seems unaccountable to the wizarding population, let alone the public at large. 

The “mudbloods,” those without wizarding parents, are not, as they may appear at first glance, a stand in for the middle class or the population at large.  Instead they’re the nouveau riche, all too easily integrating into the system by marrying them into a down-on-their luck old magic family (e.g. Ron and Hermoine.  Voldemort’s attempts at revolution are battles within a ruling class and not indicative of a wider societal struggle.

How could reform come to the wizarding world?  Spoiling Harry Potter 7 a bit, a goblin ripped off by our heroes would need to realize that the fact that goblins haven’t developed a system of presently [permanently] transferable property rights hasn’t stopped anyone else from implementing such at their expense.  Thus, the solution is not fighting old battles to regain lost artifacts but instead the introduction of planned obsolesce. 

Mass produce lower grade magical items, the sort that will not be around generations down the line, which in means that it’s no great loss to goblin-kind when they aren’t returned upon the death of a wizard.  This mass production could in turn lead to the rise of a wizarding middle class, those who lack magical talent but who could achieve great productivity benefits via clever uses of weak magical items.  Until such a class developed, there’s no popular basis for reform and as the epilogue of Harry Potter 7 showed we certainly can’t count on the heroic elite.