It all depends on what happens to you and the state of your body. For instance, don't expect any financial sympathy or support if someone drives over you at a pedestrian crossing. Or if you have a heart attack. Taking a risk is fine until it's not. On the other hand, travel insurance is ridiculously expensive now.
Seemed to me in Pattaya some years back that the volunteers were on the beat with the local police. Certainly they were not involved in backroom or immigration related work. Perhaps someone in one of the 2 places who is familiar with the current set up would care to comment. I have expressed my opinion.
A lot of the volunteers are found in places like Pattaya or perhaps Patong in Phuket, where the police are often corrupt and out to fleece tourists if possible. I have personal experience of police in both places and would have little respect for a tourist who chose to work with these people.
I stayed in an apartment near On Nut BTS last year, one of 3 areas of Bangkok I experienced over a month. I think it's a good area, fairly central or at least well positioned in terms of public transport, well serviced by department stores, markets and restaurants. I lived in Bangkok for 6 years back in the 90s before the sky and sub rail and drove a car. Public transport has improved out of sight since then.
What sort of foreigner would want to volunteer to work for the tourist police? It's like classmates at school that became prefects then reported you for not wearing a cap etc. Scum.
If you can get it but can't use it what is the point of it? I'd have assumed form the question that the person was hoping the insurance would be usable.
You certainly didn't get much refunded by Cigna. I gather you also would have been refunded little if anything for the surgery and chemo, hence your decision to return home?
Cost me all up $1000 to have a cancerous spot removed from my face in Australia and got nothing back on Medicare because it is regarded as a cosmetic operation! It's precisely the sort of problem that would be better to have done in Thailand assuming that you paid significantly less than I did. I had a femoral hernia operation done in Cambodia in 2019 for $US450 because I knew I would wait 6 months back home and the condition was uncomfortable, as well as a bit dangerous to travel with in SEA. Not that any of this discussion helps answer the OP's question. My query would be does overseas health insurance cover such conditions as skin cancer or treat it as a known condition as with hernias and travel insurance.