First of all Cloudflare does not disclose to excluded communities why they are excluded. This non-transparency keeps the marginalized in the dark about both the technical criteria for exclusion and also the business reason for exclusion.
Why I personally have been excluded is irrelevant trivia. The full extent of CF’s exclusion is unknown but it’s evident that at a minimum these groups of people are excluded:
public libraries
Tor users
VPN users
CGNAT users (often poor people in impoverished regions whose ISPs have fewer IPv4 addresses to allocate than the number of users)
people who use scripts to access web resources (and interactive users who merely appear to be bots by using non-graphical FOSS tools, blind people IIRC as they are not loading images)
all people with a moral objection to exposing ~20—30% of their web traffic (metadata & payloads both) to one single centralized tech giant in a country without privacy safeguards.
I personally experience exclusion by all of the above except CGNAT.