This results in a major inconvenience in modern society, since people are expected to do things in their daily lives. In other words, there was a need for ways to manage this bodily function, and so came sanitary options.
Traditional sanitary options are meant to be temporary placeholders that absorb the fluid and are quickly changed when saturated, leading to unsustainable resource waste and inconvenience in daily life. Imagine how inconvenient this would be in the case of other bodily functions, such as urination and defecation! (Yes, I know that incontinence exists, but unlike menstruation, incontinence is not something that a significant portion of the population has to deal with.) But in the case of menstruation, it is commonly seen as the only way to manage menstruation.
The menstrual cup is theoretically a smarter idea because, in the absence of an internal storage receptacle in the body to store menstrual fluid until it can be dealt with at a convenient time, mankind has invented an artificial one. We are filling a need that nature has forgotten to fulfill, in the way of how nature has fulfilled similar needs. After all, why reinvent the wheel, as they say?
tl;dr OMG MENSTRUAL CUPS ARE GENIUS