Comment by mschuster91

The answer to this is government regulation. Here in Germany, ever since 2016 we have the "Routerfreiheit" codified in law [1] - despite numerous attempts from wannabe crap-peddlers and cheapskates over the years, it still stands strong. Just this year, it was confirmed again, that the freedom to choose your router even applies to GPON [2].

ISPs here are required by law to state the technological standards they use, and consumers can request the required authentication data (for DSL PPPoE) or, in the case of hardware-based authentication with MAC addresses (for DOCSIS), submit these to the provider.

In practice most will rent from their ISP, but the competition is so strong that cheap crap routers are rare, usually ISPs make a point in advertising customers will get an AVM FritzBox - the ultimate market leader for good reasons.

[1] https://www.bmwk.de/Redaktion/DE/Artikel/Digitale-Welt/freie...

[2] https://www.teltarif.de/bnetza-glasfaser-routerfreiheit-netz...