I always found that idea funny. For most people the most important thing over the course is working days and time off days. When do they have to get up, when do they have to work, when do they need to get going early, to get to some work location, an office maybe, and when do they not have to work. Saying that "the week starts on Sunday" makes me immediately think: "Oh, you start working on Sunday?". In most people's minds in my bubble the work starts on Monday, which makes it the more natural start of the week, at least I would argue. To me personally starting the week on Sunday seems removed from most people's job and work reality.

In many calendar applications one can actually configure things like that. Often the option is directly named something like "start week on Monday/Sunday".

We also shouldn't neglect the fact, that other cultures other customs. Maybe the week starts on Sunday in your location, maybe it doesn't in my location.