I love that blouse and would love the pattern as well. Should it come out in print, I'd be buying it! I'll give you a bit of "teacher" thoughts on the pattern and making it available.
First of all, when you develop a class and pattern, it takes LOTS and LOTS of time - particularly if it is a unique pattern. It takes me a couple months of dedicated work, testing samples, etc. not to mention writing up the instructions and the diagrams or pictures needed for that. After all that work, if you love to teach, you do hope that guilds/groups will invite you to teach that particular pattern. If it is available right away, that might discourage individuals from otherwise taking the class. So, to hold back on making the pattern available for a period of time may be a good business choice, though I could definitely see the argument for the income made from online sales. :) As was mentioned, everyone cannot take a class, but would probably love to purchase the pattern. I do think that the sales would be there.
Additionally, it could be the expense of producing the pattern for selling and hopefully making a profit. Just this last year my printing costs for pattern tripled from March to Sept. making it unthinkable to offer any patterns in print form. A pattern that I had printed in Feb. for $5 now costs $15 - and this is the BEST price I can get anywhere unless I want to order hundreds at a time (which involves a huge cost upfront, storing patterns, etc.). Add to that the cost of printing the instructions, the plastic bag and the time to fold the pattern and assemble the patterns for sale - no money could be made. So, unless the pattern was made ready as a PDF, there won't be any patterns for sale from me. to make it ready as a PDF will require hours and hours of work on the computer. I may decide to do that for some of them. We'll see. It has taken me forever to learn how to do the patterns on the computer and I doubt I'll get quicker at this any time soon. for someone trained and knowledgeable on the computer, it would take less time, but still would be a significant time investment.
I only have one of Trisha's patterns from a class I took last year and it didn't have any real pattern pieces - only an armhole - so that one could easily be made for sale (my opinion) and money could be made from sales. However, I would assume that this blouse pattern would have several pieces that would require printing. Without that information, it's hard to say.
It's easy to have a strong opinion regarding things like these, but as I've done more and more pattern work, I have a different perspective than I did prior to just being a student. :)