The thing is O has never been a big part of the market (and I'll quantify that in a second). I am sure some will point out that at one time Lionel was "it" and HO was a small thing, but that changed a long, long time ago, like by 1960's. HO and n have so much made for it that there is a huge market, and it isn't surprising. Given the constraints of O (cost isn't as much of an issue, HO and n scale equipment has gotten surprisingly expensive these days) with size and space, HO and N are more 'natural', you get a lot more done in a smaller space.
Anyway, I have been reading MR for many decades, and O has always been, if not a side project, a very small part of the market. The Walthers N and HO catalogs were huge, O was in comparison an advertising brochure practically. So what we see in this world is not new. I would hazard that 80-85% of train modelling is HO/N, and honestly has been for a long time. Manufacturers like bulk, for obvious reasons, lot easier to recoup costs and make money. It is good for the consumer because you get competition (take a look at the DCC world with command control for example).
In other words, O is what it always has been. One of the largest costs for a kit or pre built building is tooling, and given the limited market for O, it takes a lot more sales to make back costs, because while they charge a premium for O stuff, they can't charge enough to make back costs as quickly as HO.
For example, assuming the tooling costs are the same between HO and N (they aren't, though there can be common parts, an HO scale window might be a small window in an O scale structure) and let's say it takes 100 sales to break even on this cost. In HO, even being really generous to O, for every 100 structures you sell, in O you might sell 10. They can't charge 10x for the O scale kit, so it is going to take a lot longer to recoup costs and then maybe make a profit with O.
And these days from what I am led to believe in HO and N most people are buying ready built structures, not kits. There isn't a huge cost savings with kits these days over a comparable ready to use structure because of the way things are being produced (I am sure some envision a person sitting at a workbench putting together the kit version the same way they would; it doesn't work like that).
It is hard to compare to the past, but in HO and N I think that a lot of people back then did kits or scratchbuilt did so because they didn't have a choice, it is what you did (it was like the 1930-40's with HO , and well into the 50's, you often had to buy kits for rolling stock or even engines, it is all that was out there, RTR became a big thing by the late 50's). These days there is such a selection of RTR that people can find what they want or they can easily modify it, so kits in general are not as big part of the market either. I think time plays a role in this for people who are still in their working years with families and such, and the other factor is that there are simply a lot of people who don't enjoy putting together kits or scratchbuilding but in past decades would have to to get what they needed and now are happy not doing that.
In terms of the companies that are hard to reach, etc, these are not big businesses, they are hobby/cottage businesses , some person doing it out of a basement someplace. Not saying they shouldn't be more responsive, but likely this is a side business they 'get to' when not doing other things, not their livelyhood. I kind of wonder if these people are like Gibbs on NCIS, they prefer the old ways of doing things, cause these days all monitoring email requires is a cheap smart phone or a tablet, or if you have a business phone, can access voice mail anywhere or even get a written alert to your cell phone from a landline phone or whatnot *shrug*.