The good docs nearly always have essentially as many patients than they want to see, but IMO, demand always comes down to skills (both procedural skills and PR skills).
If you can only do basics like nails, orthotics, heel pain conservative treatment, and padding... well, you might not be in real high demand. Don't get me wrong: you will still have a ton of patients with those common complaints and needs, but if there's 100 other guys in your city who can do what you can, you see the potential problem.
If you can add bunions, hammertoes, advanced heel pain modalities, neuromas, etc to your service offerings, then you will attract more patients. Still, everyone coming out of residency today can do those cases.
If you can routinely handle complex flatfoot reconstruction, pediatric developmental abnormalities, rearfoot trauma and ex-fix, flaps, etc with good results... well, you have elite skills. Chances that other pods - or any kind of docs in the area - won't have the level of knowledge that you do.
Also, it often matters more what you are "known for." That will get you referrals. The simple fact that you can do a Charcot foot reconstruct or a PCDO with TAL does little good if most primary care docs in the area don't know that. Sadly, I've seen a few docs with great skills or a very sharp diagnostic eye who have a tough time filling their appointments due to networking difficulty. Some of that can be the fact that it does take time to build a reputation, but being outgoing and a good communicator is still essential even for an established practitioner. Networking, establishing a reputation, and carving out a niche are key factors and recurring themes that you will quickly notice in many highly successful and renowned DPMs.