Well so a few things here. Unless you have alts on every datacentre and have gauged opinions from all players you come across, then what you hear in-game isn't always enough to give a clear picture. Same with the forums, only a small population of all the players in the game actually use this place, so again we wouldn't have enough to go on. Also it's easy for negative things to gain traction because if people are happy, then don't have much reason to complain. The updated TOS is a example of this, the Western playerbase is being very vocal (we have a thread nearly 30 pages) whilst the JP players are quite content with it (thread with a couple of pages in comparison I believe).
You are right no one asked specifically for Limited Job, but it had also never been done before so you can't really ask for something we knew nothing about. Players wanted BLU to be added, but the devs decided that could only do it one way and that's what they did. Though as I said this might change in the future, but for now they are experimenting with the "Limited" tag to see how it works as an in-game feature and take feedback from the players. We might see more Limited Jobs or maybe none at all with BLU become a full Disciple of Magic job, it's still early days.
BLU isn't a mini game per say because it still has access to a degree of content just like all the other jobs, except currently there are certain limitations to which the Masked Carnival is probably supposed to fill that void. If players wanted more solo content to justify its existence they would just wait for the Trust system in 5.0 where players can do duties with NPCs, they have no reason to expect BLU to be the provider of more solo activities (it can still do things in parties after all). Right now BLU IS a job but with restricted options available to it (hence "Limited"), stating it's a mini game would be a lie, you'd find those in Gold Saucer.