Any company where understanding of security practices has a direct impact on its revenue from early phases can be considered as a security company in my view.
From what I have seen a large chunk of internet exists and stands on the shoulder of folks who did the volunteer work cause they were passionate about it and enjoyed that part. Once built, the nominal fee for API to check IP address should cover the costs way easily for the servers.
Letsencrypt is a great example, it did took away the big money from all these commercial CA's, who used to issue blue, green and what not kind of checkmarks. Thats one big reason reason why the migration to HTTPS happened faster.