Tunneling isn't that big of a toll on resource, it doesn't require storage/disk space nor compute power (CPU chips), all it needs is ingress/egress (spare bandwidth). A non-profit or decent business in telco can easily offer it, consider that many hosting companies offer entire package in free tier today (compute + disk + egress).

For several years, ngrok was practically free, only recently they've started monetizing once it gained popularity.