There are so many different threads at work affecting OWR (and all amateur racing for that matter). To highlight a few from my perspective (~45 years racing, 39 in OW):
1) Too many classes (FA, FB, FC, FM, FE, FE2, FF, F600, F500, F1st, FV [F4, F3], did I miss any?) create confusion and dilution both to existing and more importantly, potential new participants. I believe there is more or less a finite number of drivers out there interested in OWR.
2) Too much resistance to modernizing or updating cars, motors, etc. to keep up with changing technology resulting in 20 year old chassis which are unappealing to new participants. (note, this is not a universal issue- FV eg, however even FE and SRF have been updated recently)
3) Costs: A big one. If you look at the list above, there are classes you can join very inexpensively (relative) or others which are inherently very expensive both to initial purchase and operating cost. Two very visible costs are tires and entries, but I don't believe they constitute the majority cost of racing a car.
A) With tires, I believe you get what you pay for in terms of expense vs racing experience. You want slicks and g force? You want longevity? The two seldom match up. Its a valid argument and there are advocates on both sides. Some classes have already acted with an acceptable spec tire, others haven't but should.
B) Entries are a different matter. Track rental costs keep going up -you wouldn't believe what it costs to rent certain tracks- for example WGI for a FRP weekend is about $78 per live minute of track time, less desirable tracks are in the $55 per minute range. The club (regions?) has little control over that thanks to car clubs and track day event organizers who will simply continue to pay whatever the tracks charge, or rents so many days they have leverage to negotiate. I would hope SCCA can negotiate.
4) Changing demographics: Fewer people are willing to spend the time or have the skills to make a formula car competitive. It takes effort to get a car to the pointy end of the grid in any class, but maybe more specific skills in OW. Maybe that's some of the reason for the proliferation of SRF and SM...
I'm sure this thread will add more reasons. The solutions are going to be a bit painful, in my opinion, but very necessary. The reference about breaking eggs to make omelets comes to mind. I have some possible solutions which I submitted to the CRB in a white paper about 2 years ago. I didn't expect them to simply adapt my suggestions, but start the conversation within the FSRAC and CRB. I believe that to be the case and the change in FB the first public indication they are taking this issue seriously.