@CursedSilicon @argv_minus_one @fivetonsflax @futurebird yep, I came here to explain this but you already covered the bases. It's a similar story with ADSL/VDSL as well - symmetric DSL variants DO exist, but they have significantly reduced downstream bandwidth compared to their asymmetric cousins. Given the general traffic mix of a residential connection, the asymmetric profiles were generally a sensible tradeoff.

Fun fact about DOCSIS: one of the side effects of grafting data service on top of cable TV networks is that all traffic is encapsulated in MPEG-2 transport stream frames - 188 byte (iirc?) chunks. Downstream traffic is also broadcast, so on early networks it was possible to see traffic destined for other customers. An encryption layer (BPI) was eventually added, giving each cable modem a separate encryption key