One of the things that is forgotten is how much of this hobby is inherited. There are a lot of modelers out there who are running trains (or at least the rolling stock) inherited from a parent or grandparent. If you go back 60 years (when I started modeling, in HO), N scale was a tiny niche market- mostly European prototype, and a few companies just getting their feet wet in the smaller gauge. "HOn2-1/2" - HO narrow gauge compromised to run on N gauge track was more readily available than N scale North American prototypes.
So, the equipment that was handed down or gifted to the next generation was HO. And, while N scale has grown a lot since those early days, HO remains the dominant scale, in part because the trains themselves have passed down to another generation.
Even when the trains themselves aren't passed down, the majority of modelers have their first experiences with HO, build their first models in HO, and... just giving up years of work to change scales takes an emotional toll- we put a lot of ourselves into our modeling, and we have a sentimental attachment. Not to mention the financial cost involved in changing scale, or adopting a second scale.
I think part of the complaint many have (me included) is that N scale manufacturing is increasingly focused on modern equipment, and those of us who model time periods in the steam or transition eras are having more difficulty finding locomotives and rolling stock. On top of which, we have the pre-order system- so we can no longer just go down to the hobby shop and pick up a couple more F7s whenever we need them. Most of our shopping nowadays is in the used or 'pre-owned' markets.
But overall, in the course of my own modeling years, N scale has gone from less than 1% to something like 30% of the US market. From a couple of niche importers, to several major manufacturers- some of whom are focused on N scale like Kato and Bluford. And several manufacturers that were once exclusively HO, have introduced N scale products. Not everything we want... but more products come out every year.
Happy 4th everyone!