Whats the benefits for them?
ExpressVPN has a large server count because some of the servers are virtual servers, meaning that even though they state that they are from a certain location they may me in fact from another location.I have been a user of VPNs for long time, have tried many however I suggest only 2 as the best vpn so far, Nord and Express vpn. Nordvpn has a very strong encryption for which I give it a plus and it's offering dedicated servers for streaming. Secondly, Expressvpn has I think the biggest number of servers which hardly any other else do have.
You can compare the features of renowned services yourself - Best VPN Service Providers for 2018 – Unblock Content & Secure Your Data