I use AWS and gcp. Both of these cloud platforms have the ability to establish a VPN connection from a VPC in the cloud to an on-premise router or another cloud VPN endpoint.

They both use bgp ( and support private ASNs) https://cloud.google.com/vpn/docs/how-to/creating-ha-vpn2 https://docs.aws.amazon.com/vpn/latest/s2svpn/VPNRoutingTypes.html

I'm curious why they chose bgp and not another routing protocol like ospf/isis. Is bgp just the lowest common denominator? is it available on more platforms? or is there a more fundamental technical reason. I'm curious because bgp has a huge a feature set and this use case is very narrow (just exchanging routes) so seemed like overkill