It even happens to ISPs themselves to get marginalized in this way. I work in a small local ISP, and we're fully IPv6-ready, but the publicly funded optical networks we use to reach our clients are not IPv6 ready. It should just be a simple VLAN, transported how they please, that connects us to our client, but no, the infrastructure operator built a mess just to connect us to our clients, I suppose just transporting a VLAN was too simple for them (we do get a VLAN, but they do some weird DHCP interception on it, and dynamically route IPs in their iBGP based on that, and didn't set it up for DHCPv6, so no IPv6 for our clients).

This is one of the biggest FTTH networks in France, where IPv6 is deployed a lot.

Of course, the bigger operators can collect their traffic straight at the OLT, so they don't have to go through this mess, and get better quality of service (the DHCP interceptors fail often) as well as native IPv6.

We small operators need to set up tunnels to provide IPv6 to our clients. Even for additional IPv4s or just anything bigger than /32 we need a custom tunnel. And these tunnels are a mess to manage when the customers have their own CPE. It's so sad, and that's all done with public money.

And yes, of course, this infrastructure operator, Covage/XPFibre is owned by Altice, who also owns SFR, one of the big four operators. How surprising.