I think that the trials bike sales# problems stem from several areas . First, the sport is just too purist in nature and is bound to be a niche occupied by the very fit young rider. Few existing riders can/will try this as there is a lot of existing competition from other forms of riding.
Second, the bike used is very specialized and expensive. It can only be used for trials work and is thus only useful in areas where there is trials terrain and a rider network. Compare this to the opportunities for purchasing and racing an MX bike for instance.I think a lot of potential age group users are turned off by the low speeds also....especially all the stopping and looking around now allowed.
Third, just try to find a trials bike shop to even look at one! You have to be an "insider" to see a real bike here and most people do not know where to go to see an event.Who is buying bikes right now? The fastest growing segment of sales is older guys buying dualsport/ADV bikes. They still have the income but see trials as a too difficult alternative in most instances. It does not surprise me at all that the trials segment has few sales. The BIG 4 gave it up in the 70s for a reason... insufficient interest.