In regards to the increasing number of schools: Perhaps it just depends on the area. I personally have yet to meet anyone in person who wants to be a farrier, let alone an actual working farrier. I did meet one fellow who said he took to trimming his own horses because he could never get one to show up!
The same fellow claimed that in a nearby county, due to retirements there were now only 2 or 3 farriers in the area and they were all booked up. I'm doubtful as there's a horseshoeing school here within a two hour drive. However, I've heard many people attending school just want to learn to shoe or trim their own horses. Makes sense with the rising costs in horse care.
An uncited statistic I read: 1 in 10 practicing farriers continue with the trade after 1 year. As a comparison, nearly every student at my welding school got job offers. Some companies were showing up and pulling people out of class. Obviously that's a different scenario, but as a former independent contractor I know that many people do not last long in self employment. It is often difficult to do successfully on the side, both from an economic perspective and in terms of skill development.
Another thought: The Post 911 GI Bill has made it far easier for veterans to attend trade schools. I recall hearing once or twice that there used to be quite a few horseshoeing schools prior to the 1950's, but a huge number went out of business after the VA decided to stop paying for them. Maybe things are simply going the opposite way?