The most profitable keywords are in industries where there is a high lifetime customer cost. Most of those are mundane because the less you think about it, the longer you stay as a customer.
I would have said the more ambulance chasing legal queries and plumbers 15 years ago when I did a bit of AdWords plumbing keywords in London where £45 to £50 quid
https://alejandrorioja.com/high-cpc-adsense-keywords/
You also see it in Google keyword prices:
https://blog.hubspot.com/marketing/most-expensive-keywords-g...
The most profitable keywords are in industries where there is a high lifetime customer cost. Most of those are mundane because the less you think about it, the longer you stay as a customer.