A two hundred hour training is not very long to learn an ancient practice of the breath, body, mind, and spirit, yet that is all that is required to be yoga teacher, and really it is not absolutely required because as of right now there is no licensing required to be a yoga teacher. That is why it is beneficial to the teacher and therefore to their students to attend as many classes as they can, go to workshops, and if possible attend multiple trainings.
That being said, yoga teacher trainings are expensive. The cost of mine in 2013 in Nicaragua was around $3,000, not including flight. The cost of my most recent training in India was much less, but still at least $1,000. Those prices may look high, but they are pretty low compared to what else is out there. When I was researching trainings I found some for as much as $3,000 for a two week, two hundred hour training (how you can cram 200 hundred hours and thousands of years of knowledge into two weeks is beyond me) which did not include any accommodation or food. The trainings listed above were both month long intensives that included room and board for the entire month. The current, official Bikram training, held at a fancy resort is $16,600 USD for a single room, the training is around two months long, therefore double the length of either of my individual trainings, but still very pricey.
Examples of costs of trainigns are to emphasize that I realize that most people cannot afford to take multiple trainings. That being said, what teachers can do is attend workshops, join studios, find a private teacher, and/or study online. Finding classes and workshops that are designed to be continued education. YMCA, power yoga classes are not what I’m talking about. Those are fine for a teacher to take to get ideas about sequencing, playlists, and cues, but in order to learn more about yoga, teachers must practice themselves and continue to study as much and as often as they can.
Workshops are great because they break poses down and actually teach how to teach, if geared towards teachers. Even if a workshop is for the general public and not towards teachers then teachers are still likely to learn something more than they would in a workout-style class.
A teacher could take every workshop and training available in their area and still not learn yoga in totality. That is impossible. What you can do it specialize your practice and teaching skills. Take workshops that are geared in what is needed in your local market or that you have a keen interest in. Areas of specialization might include prenatal, vinyasa, alignment, etc.
Once you get to a workshop make it worth as much as you can, ask questions, introduce yourself to the teacher and other students, network, and practice hard. Take handouts and study them. Take a notebook and pen and take notes. Treat your workshop time as you did your teacher training time and study.
Self study and being a forever student is what a yoga teacher needs to do to better their own personal practice and therefore to improve their ability to teach their students and to continuously offer more. A stagnated teacher leads to stagnated students, and yoga is about progression.