That makes sense if you like numbers that are easy to multiply and divide, but it depends on region. Some people aren't familiar with metric, and the recipes they write probably don't use it. In all likelihood, recipes you find in imperial units were likely written by an american.

The volume vs. weight thing though, that transcends region or systems of measurement. It assumes everyone has a kitchen scale, when most non-professionals have volumetric measuring supplies which are typically way cheaper