I have been closely involved with the retail decisions about materials with two different shops, and I think I can tell you some reasons why a shop might or might not push jacket BCDs (or really anything).
1. Depending upon where you live and what kind of diving is done there, the shop might believe that BP/Ws will not be big sellers. They do not want to have unsold inventory on hand. (I can absolutely guarantee that this is the primary reason in my area.)
2. Some of the most popular BP/W makers require that shops enter into a contract with them that requires an initial minimum order and a minimum annual purchase of their products. Both shops I have worked with will not sell certain brands because they cannot make such a commitment.
3. Most shops have contracts with certain vendors as described above. They need to sell a certain amount of $$$ for those vendors. Many of the most popular vendors either do not make BP/Ws or they make one that people don't really want. If they enter into a contract for BP/Ws with a vendor that does not have a high minimum sales requirement (and there are some), every BP/W they would sell from that company is something they are not selling for the companies with which they have the minimum sales contracts.
4. Even if a company is easily meeting minimum sales quotas for a vendor, there is an incentive to sell more, because the company will charge lower wholesale prices for higher volumes of sales. That even goes for specific models of equipment. The shop I used to work for makes a HUGE push to get customers to purchase a specific BCD, a specific regulator set, a specific fin, a specific computer, a specific wet suit, etc. Their instructors are required to purchase and use those specific items when they instruct, and they are required to tell the students that they made those choices because as professionals they demand the best. The real reason is that that package of gear gives the shop the highest profit margin, and by increasing the volume on specific items, the profit margin is made even greater. (That is one of several reasons I no longer work for that shop.)