There clearly are not enough organisations running seminars, it basically a cartel.
Anyone is at liberty to apply to run a Seminar however it has to meet certain JAA requirements regarding content. That means that you have to have a number of presenters with the relevant experience; if you include helicopters that increases the number of presenters. They need to be paid and so does the venue where these are held. There are currently around 7 Seminars a year and a unexpired FI may attend at any time in the 3 years of rating validity. If each Seminar offers typically 40 places (some have catered for more) there are 840 places available; now as you can only revalidate by Seminar every 6 years, that means 1680 instructors are catered for. Supply exceeds demand.
Initially there were 4 potential providers, thats before the JAA effectively halved the number of likely attendees. One failed to meet the grade, another ceased trading and the 5th has never offered a Seminar. In order to recover the costs you need to guarantee at least 25 candidates, some Seminars have run on less than that. I would suggest that its a free market and that the supply currently exceeds demand which from an economic point of view is likely to deter any new provider. Instructors need to get there act together so that they take advantage of the available Seminars rather than waiting till the last minute and them blaming everyone else.