Shouldn't there be a more beginner-friendly approach to offering private lessons? I mean, most of my local studios/teachers don't have brochures/flyers/websites listing private lesson package specials and explaining/comparing with group classes. If privates are really so efficient for learning, wouldn't it be helpful to explain that? If I know that, say, one private will teach me as much as four group classes, it's something I would definitely consider.
I think it may be a matter of simple cost. Lets say a local teacher teaching in their own space charges (on average) $50 an hour for a private. (about the going rate around here for local teachers working independently or a private through a studio.. ranges from $40-$60) And that same teacher can accomodate 10 people in that same space for a class. Class rates would typically be around $10-$15 per person.
So in an hour, the teacher makes either $50 or $100+.
Why promote privates over group classes and lose money considering that few (if any) of those 10 students from the class would take privates
weekly to make up the cost from not having a class.
If the teacher works out of a ballroom studio, they will have even less flexibility even if they preferred to make less $ and work with individuals.. the studio will want the biggest classes it can get, especially in this economy which is hurting non-essential businesses. Evenings are pretty full on the schedule. The studio isn't going to let the teacher have a room for a private unless there's just nothing else going on. They aren't going to let the teacher bring in $50 (some of which has to be given to the teacher!) when they can make at least $100 (minus cost of teacher)
So the studio allows scheduling of privates on in "empty" slots that they don't schedule classes... ie: middle of the day during the week. Not many people can do that, and the unemployed people who ARE free can't afford it. (Some studios have free space on weekends during the day.) Teachers will have to give some of the take to the studio, and if they have a relationship with the studio from teaching a class, there may be issues over teaching privates OUTSIDE the studio on their own.
As someone who prefers to teach privates, and tries to promote myself that way, I find that if you aren't, at the very least, a teacher who has a regular weekly class or two, its hard to get anyone to take from you. The thinking is that if you are any good, you'd have enough people for a class.

Few people want to try out a relatively unknown teacher through a private as a beginner in that dance. They want to go to the group class first and check it out. The teachers who REALLY get the most people seeking them out for instruction are the ones who are
event organizers as well as group class teachers.
There is also the problem that people usually can't afford a private every week. People who take from me do so in a rather sporadic fashion. They also take from others and from every guest who comes through town (and we have a lot!) You don't get a reputation as a teacher without students that people can point to and say "S/he is So and So's student... Wow!" No one who takes from me is exclusively MY student.
The issue of not being able to afford it regularly I think is another reason why no one should
have to rely on privates exclusively as a beginner. No matter how good the teacher is, one lesson a month (or less!) is not a good way to start a new subject for learning. Intense instruction less often is not retained as well as less intense instruction
more often. An hour of a teachers undivided attention is fairly intense for many people... They get a LOT of feedback compared to what they get in a class... and they EXPECT a lot of feedback.... that's what they are paying for.
Beginners would learn better doing 20 minutes of instruction 3 times a week, than 1 hour every week, and certainly better than 1 hour every month. If you've got someone for whom money is no object that can pay for a weekly private (or more!) as a beginner, then sure... why not...
But who's got that kind of money these days just to TRY a new hobby?