I can see the point in having a shared experience of Yoga and having somebody to examine if you are doing the posture properly, which is why I said that it is useful to attend a few classes every now and then, to make sure you are doing it correctly.
However, I feel that the notion that we must attend classes regularly is overestimated and perhaps based on some self-doubt, that we are not doing things correctly and constantly need supervision. I mean how many classes and realignments do you need before you feel your downward dog is OK, and feel no need for more realignments?
I think one of the reasons the Yoga industry exists is because there is this constant realignment business going on - no matter which teacher you go to, they are probably going to realign you, even if you had already been realigned by your older teacher. This puts doubt in ones mind that their practice needs to be constantly realigned till it is perfect. But isn’t the truth that your downwards dog will get progressively better itself the more and more you practice - it will eventually fall into place.
In the Yogasutras Patanjali talks about the asana as eventually falling into place as you practice, you eventually find the right way to do it that suits your body. You feel what is right for your body. A teacher probably thinks something else is right for you, but they can’t feel what you are feeling. Only you can really know what is right for you.
Hence, my point is that I think the need for attending classes and having a teacher is overestimated. In the many Yoga classes I have attended, I have not really felt a huge difference in doing my practice in a class with a teacher and doing it at home, except that when I do it at home, I am a lot more comfortable and more in-tune with the rhythm of my body - and of course I save money.

It is their ignorance vs 2000+ years of history of Yoga.