Well, I'm another native speaker and it doesn't sound horribly awkward, but once you chew on it for a second, it gets ugly.

One, the problem with 'demanding' is not that it is 'vague', it is simply the wrong word. They mean "competitive" and you cannot in any way use 'demanding' to replace it here. It is simply wrong. The 'demanding industry' collocation exists, but it doesn't work or even make sense here. No native speaker editor who thought about that sentence for a second would allow that because of the second part of the sentence.

The first part of the sentence is talking about the english teaching industry, but the second part is referring to student satisfaction, hence it creates this creeping confusion which builds as your roll it around your mouth some more. Furthermore, "the satisfaction" is completely unacceptable. We simply don't use 'the satisfaction' as a noun that way in english, it needs to be paired with something as the other commenters stated. So, no, it is not unclear who's satisfaction is increasing, but it is made 'awkward' by having the first part of the sentence referring to gaba itself, combined with the usage of 'the satisfaction'.

I think the big thing is the 'demanding'. That just screams out, wrong. The awkwardness of the second part could be 'overlooked' as ad-speak, but put all together, its reaches total fail. F- for you GABA! Back to night school!

Finally, even ad-speak english reverts to the most colloquial. I think we're just more comfortable with the least formal speech. So, of course, all this 'increasingly, satisfaction, blah, blah blah,' works, sometimes still seem awkward since no one in real life would ever say them.

Why are students increasingly satisfied with our classes?
Why are more and more students attending/coming to our classes?

Less formal yes, but more in-use and hence less 'awkward.'

Anyway, the important thing there can be no logical connection that they are trying to draw between (demanding industry) and 'satisfaction', that is simply an incorrect use of demanding and it fucks up the whole thing. And even if they changed it to 'competitive' the sentence would still be too busy and trying to do two things in not a lot of space with not a lot of logical connection. Awkwardness is dying to come out there. FAIL.

And yes, level of satisfaction is not only better, it may be near-required.