I do not know the specifics of the situation, but I can talk in generalities. 
There’s knowledge that is built on other knowledges and practices. For example, for industrial applications of arsenic, you wouldn’t just teach them to use arsenic - one needs to know a certain laboratory principles, and the dangers of arsenic, before you tell them to handle such lethal materials.
And it is the final step.
Right View comes first, so on and so forth.
Specifically, jhanic experiences can be overwhelmingly blissful, and furthermore, can be a door to mind-made realms and experiences as told in DN 2.
These are extreme experiences by any measure of the word. In itself, they can be both useful but also harmful, depending on the practitioner’s conditioning. Much like arsenic, which although has legitimate uses, is highly dangerous.
Therefore, there’s prudence in limiting the public retreats and practices to most basic forms of practice. There’s prudence in focusing on basic Ethical training, which I also think would help most people before they’re introduced to Jhānas.
MN 143 is a good example for this:
When this was said, Anāthapiṇḍika the householder wept and shed tears. Ven. Ānanda said to him, “Are you sinking, householder? Are you foundering?”
“No, venerable sir. I’m not sinking, nor am I foundering. It’s just that for a long time I have attended to the Teacher, and to the monks who inspire my heart, but never before have I heard a talk on the Dhamma like this.”
“This sort of talk on the Dhamma, householder, is not given to lay people clad in white. This sort of talk on the Dhamma is given to those gone forth.”
Although, again, Anāthapiṇḍika was also just a lay follower as he received this teaching.
So, there’s nuances and edge cases to rules always, but the main point is, just like a university course has Year 1, 2 and ao on courses that build up on one another, Jhāna training is presented as the final step of the N8P, that’s fruitful once all the other factors are in place.