This is the generally correct answer for most time divided (tdm) services. I worked on dsl back in the 90s and we experimented with pretty much all the flavors

This is the generally correct answer for most time divided (tdm) services. I worked on dsl back in the 90s and we experimented with pretty much all the flavors (SDSL, ADSL,etc) and while some of the plant that was built to recent modern standards could handle a maxed-out capacity, a lot of the plant (50-80+ years old) simply wasn’t suitable for it. Telcos had a choice - give everyone the lowest common denominator, deploy multiple solutions to different neighborhoods or overbuild the plant with new plant. Verizon largely chose to do the later and you got fios as a result. Other telcos did overbuilds as demand materialized. Regardless of the technical later you still had the commercial offering to consider. One way to preserve “business” line economics was to create an asymmetric residential offering. For the most part it also reflected the underlying technical capabilities. WDM fiber I don’t see happening as a residential offering anytime soon. With current technologies 200G per wavelength is capable but the card costs alone for that level of service implies many thousands in monthly recurring to recover them. 10g cards obviously are lower but gpon is much better suited as a residential architecture both economically and technically.