I should add in case it wasn't clear: to a certain extent you're also very correct. Everyone is different and the amount of weight a person should lift is individual and can absolutely vary due to a wide number of factors.

Just, from my experience, most people who's primary focus is endurance sports (or really anyone who isn't competing in a strength sport or is a teenage boy), tend to underestimate what they are capable of in the gym and/or do a token amount of weight lifting that ultimately isn't going to do much for their fitness. This is doubly true of women as there is still a stigma against women strength training (although it is going away). Of course, if your goal is to be an elite cyclist and not general health, this isn't a bad thing as strength isn't necessary for your sport (unless you're a sprinter). But for most of us, if you want to make a significant difference in your strength and/or muscle mass you have to put the time and effort in.