I think OP may be over-looking something obvious ... maybe people just aren't that interested in a Poker class?

A few arguments why this might be the case:

1. through WPT, ESPN, youtube etc, it's easy to get access to poker pros to hear their war stories ... i.e. it dilutes the draw of "experts"

2. good (not great) poker strategy is pretty simple ... play premium hands aggressively pre-flop from late position; following that advice would get most people to break-even, but, that strategy can be boring (lots of waiting around)

3. most people play poker for the social element (i.e. to get drunk and suck out on their buddies) ... improving this usually means finding ways to encourage your buddies to drink more

I definitely agree that marketing is hard ... but, when you've made a good-faith effort to get the word out, and nobody is biting, it may be time to "pivot" and find something else to sell.