It grew out of many countries licensing the specific devices at national/trans-national level, not telco level.
Though there were throwbacks, like early iPhone, with special tariffs, but those were 95% for business reasons not explained to end buyer and 5% for marking the terminal in network as "the one that is slightly out of spec and remember to special case call redirection"
True I guess, although one would perhaps expect a fibre network to be more reliable and stable than a cellular network.
Why would a large ISP allow customers to bring their own ONT if it means higher chance of problems on the PON? It doesn't seem worth the reputational risk. Allowing customers to bring their own router doesn't affect other customers.
Though there were throwbacks, like early iPhone, with special tariffs, but those were 95% for business reasons not explained to end buyer and 5% for marking the terminal in network as "the one that is slightly out of spec and remember to special case call redirection"