For starters from a manufacturer standpoint, there are far more HO modelers than O gauge, meaning the companies can justify new products and development because they will make the investment back. There's basically one operating system for HO, whereas in 3-rail we have two, with no chance that Lionel or MTH is going to surrender their profits to the other company to have one single operating system.
Secondly, there's a mindset difference between the participants in dfferent scales. HO has always been more prototypical and more a "modeling" scale. The Railroad Model Craftsman and Model Railroader magazines every issue have articles on kitbashing, scratchbuilding, repainting, etc. despite the much broader selection of available products.
The 3-rail modelers expect their products ready made, ready to run. If something hasn't been made, instead of doing it themselves, they grumble and complain about why something hasn't been made. This is reflected in the amount of detail parts and decals still available in HO and N scales, that ARE NOT available in O scale. There are 3-railers, like myself, who do this sort of thing, but obviously not enough.
When I got back into the hobby some 25 years ago, the HO guys were the first to comment how they liked my trains. I'd ask why and many times was told "you're the very first Lionel guy we've ever seen doing scratchbuilding, kitbashing, and repainting." 25 years ago repainting Lionel trains was something of a criminal offense.
Thirdly, I don't know how many times an adult HO modeler has said he got his start with a Lionel, Marx or American Flyer train set. As the 3-rail hobby has grown towards mimicing the prototypical aspects that have always been in the HO hobby, it has become far more costly. These new HO trains are expensive too. But there's a sticker shock aspect when it comes to bringing new people into the hobby.
Far too many times, I've read grumbling comments on the train forums how the emphasis on starter sets and lower cost products will deprive the 3-rail scale enthusiasts of new products, which is not only inaccurate, but short-sighted.
The new low cost control system Lionel has introduced in their starter sets shouldn't be overlooked as a new forward development. I think this will go a long way towards helping to introduce youngsters to the hobby. So often, Lionel gets overly criticized for their licensed products, their retailing and marketing and even their TV appearance on the NBC Today show. Everything they do is helping to expand their market base, which makes it more possible to make some of the high end products that do not sell in same quantites.
These expensive high end HO products are not going to children (as with high end 3-rail products): their going to adults who can justify the expense. I know of very few instances where children got their start in the hobby with a HO set (though there was Tyco with the Lionel inspired products). Most get their start with a Lionel set. So their needs to be a balance between the technology and the cost factor to not scare people away anymore than already happens.
I personally don't conern myself with the technology. I don't use a digital command system and am quite content with that. I run trains for fun, not frustration. And for me, repainting, kitbashing and scratchbuilding is also part of the fun.