I can get a bit windy, so beware. I'm also a student of history, women's studies, anthropology, and sociology, so this reflects that.
It's basically my thoughts about the question, "If menstrual cups are so great, why haven’t I heard about them before?"
Well, there are a couple of reasons for this. First I'll go with the more obvious.
Since cups are a reusable device, which can last for 10 years or more with proper care, the profit margin isn't as great for the companies selling cups. This was something that seriously hurt early cup companies (Daintette, Foldene, and Tassette inc. –makers of both the Tassette and Tasaway). These early cups were introduced in an era when disposable menstrual products were also emerging, and couldn't compete with the "convenience" of disposability.
Think of companies like Kotex and Always. Since they sell boxes (or bags) of disposable products that you use once, and toss, you have to continually buy more each month. It is recommended that you replace a tampon every 4-8 hours (for the sake of easy math, let's say 5 hours). The average period lasts about 6 days. 6 (days) times 24 (hours in a day) is 144 hours that you will be bleeding per cycle. 144 (hours) divided by 5 (hours recommended to use a single tampon before changing) is 28.8 tampons per cycle. From my brief perusal of the internet, I'm calculating the costs per cycle as about $10 on tampons (and many use pads as well). The average cycle is 28 days, which means we will have 13 cycles in a single year. That's $130 that you will spend on tampons in a year (and I'm sure that's a VERY conservative estimate).
Compare that to the average cup, which costs $30 and lasts at least 10 years with proper care.
The second reason may be less obvious at first glance. It can remain invisible to use because it surrounds us so much, we see it as the "way things are" and don't question it. As Ralph Linton said, "The last thing a fish would ever notice would be water." What I'm talking about here is our cultural attitudes about menstruation. Menstruation is considered unclean. According to Leviticus 15:19-24, a menstruating woman remains unclean for 7 days, and anything (or anyone) she touches also becomes unclean for the rest of the day. Ours is a very Judeo/Christian culture. I'm talking here about America, but I'm sure many other places are similar, and the Koran stipulates similar rules regarding menstruation (Christianity and Islam are the two most followed religions on the planet.) I know many people no longer take the Bible or the Koran literally, but it would be folly to assume that they haven't coloured our attitudes at all.
The companies that put out disposable menstrual products have also spent decades cultivating the idea in society that anything connected to menstruation is irrevocably disgusting (or shameful, or embarrassing), and that anything that comes in contact with menstrual fluid needs to be immediately disposed of in order to maintain sanitation and hygiene. It takes quite a bit of knowledge about and comfort with your own vagina and menstrual cycle to be successful with cups, and even today, most women's "nether regions" remain a mystery, even to themselves. Add to that the social taboos on a woman touching herself down there, (applicators on tampons were invented to save the woman from having to actually come into physical contact with her own vagina), and that many people are reticent to even talk openly about menstruation, let alone reusable menstrual products; is it any wonder many have never even heard of cups?
Times-they are a changin'
In the early days, a woman would probably not discuss menstrual issues with friends. Many women who began menstruating in the 1970s or earlier can even attest to the fact that they couldn't (or wouldn't) discuss the issue with their mothers. This has been becoming progressively less of an issue since the 1960s-1970, which saw the emergence of many grassroots women's groups springing up to help bring women's health and reproductive issues into the hands of women themselves (instead of doctors and insurance companies). This produced more acceptance, to not only discuss menstruation, but to allow women to become more comfortable with the workings and mechanics of their own bodies.
I began menstruation in the mid 1990s, and had no problem discussing sex and menstruation with my mother, though I probably wouldn't have (and never did) discuss it openly with friends until this millennium.
This is not the only paradigm shift that is changing the fate of cups. Disposables first emerged when advertising and a push for consumerism was sweeping the country in response to the economic depression of the 1930s and the Second World War. This spirit was continued in the 1950s when capitalism and patriotism were enmeshed in the "American dream" lifestyle, centered around the cold war and opposition to communism.
Now, we're in the middle of another economic downshift, and we've seen many of the effects of our consumerism on the environment (global climate change, pollution, destruction of natural ecosystems, and threat of extinction (or downright extinction) of countless species of plants and animals. This has also increased our awareness of how the products we use affect our own immediate (or near immediate) health, and many women are finding a product that is healthier for the environment, themselves, and their bank accounts to be very appealing right now.
PS-Not sure how I'd tag this one, so I didn't.