I’m a bell customer in Canada and it used to be the case that the ISP provided modem had a CPU too slow to run PPPoE at a gigabit despite the ISP selling plans up to 1.5gb/s (it could only do 600mb/s or something but don’t quote me). That model has a sfp ont and so you could swap it into something else with no hacking but now you can only get the model with the ont built it. The new model is better hardware wise but just as bad software wise so it feels like a step back in practice.
I think selling users SFP ONTs is probably the right balance of ISP control vs allowing customer freedom