Yes, my point was that you cannot "just" use your own equipment. There are many hoops to jump through.

Also, most widely sold Unifi equipment is expensive, cheaper devices are very rare to find in limited markets.

I would not consider this available if I have to order it from another country and pay customs + wait weeks for delivery.

And again, the equipment has to be whitelisted by the OLT and most ISPs don't want to that. And cloning the S/N is difficult/impossible.

I think we have two different kinds of ISPs in mind. I'm talking about mass-market monopolies, and you're talking about "artisanal" small ISPs where you can walk into the CEOs office and pass a rack of routers on the way there.