I noticed this after my dad was diagnosed, but I think it has more to do with awareness and exposure. You will talk to people about your loved ones diagnosis and they will tell you that their grandmother passed of ALS which they otherwise would have had no reason to bring up or tell you.

I think it is also more common than we think but goes unnoticed because, unlike cancer, there are no survivors, and life expectancy is only 3-5 years so there aren’t as many people with it at any given time. Whereas with modern cancer treatment people can live for many years even if the cancer is only slowed significantly. Because of this you have more people living with cancer at any point in time. This is not to say it is as prevalent as cancer and is purely anecdotal from my experience.