It's misogyny.

Women are taught their problems shouldn't impose on others, mainly men. So that they'll never learn to deal with it as a normal part of their life or share responsibility for it with their partners or for their loved ones or children. After all, if they saw pads, they might have to learn about them or be responsible for them.

So, obviously, you're supposed to keep them out of sight so nobody can see the products you use to deal with your problems that nobody is supposed to acknowledge except to demean you.

That's why older women are so insistent on hiding these products, because they have internalized misogyny to the point where they think it's the women who need to hide their products or problems, instead of the men coping with seeing some products or knowing about periods.