Honestly, we can all pretend otherwise, but the real reason that the colleges have yet to fall is partly that, after being organized by Teclis, they are too tough to cleanse. They did survive a standstill with the Empire after all.
That does not mean the Articles should be flouted. They are generally sensible, and only sorta, maybe, perhaps fail to work in super niche situations that are often arguable anyway, plus they work well to enforce unity within the colleges by clearly defining what a Black Magister is- without them, they may very well fall apart in civil war and become easy pickings, and they will also probably lose all support. Plus, the colleges seem to find workarounds when the ultra niche situations rear their head, even in canon (that dhar studying black magister in canon no one was in a hurry to depose and who was accepted back after he finished his research and proved noncorruption in the Felix and Gotrek novels has been brought up multiple times.)
But if the colleges weren't a major pole of power within the Empire then they would have already been rid off. The Sigmarites can argue all they want, they ain't winning that war, they didn't last time wth Dieter, they won't next time. Sure, the wizards aren't winning it either, and the cost of it may be greater for them, but my point is not that the wizards are the strongest, my point is that getting rid of them is not really feasible realpolitik wise considering their power, no matter what gets voted.
Heck, anyone looking at the balance of power of the Empire from outside would be confused as to why the colleges do not get 1- or even 2- votes at the Elector's Meet, considering the power they de facto hold in practice.
