Then you look at the product and it's nearly twice as expensive as Amazon, if you are willing to get 6 pairs of underwear at once. So who does this target? People who are too poor to afford 12 socks at once? Not compelling. Amazon is trusted and less expensive. Where is the value add?
Not having to think about it, click any buttons, do anything, remember anything, etc. Buying socks and underwear is one of those tasks that's very, very easy to perpetually put off until tomorrow.
To put it into perspective, using Hanes crew necks (that seem to be a baseline for comparison) you're paying a "discounted" $12.99 for a 3-pack on Amazon. Not including shipping -- or what you pre-pay using Prime -- that's $4.33 a shirt. Manpacks lists them at $5, with free shipping on orders above $30.
If you just don't see the value in not having to think about or shop for the basics, then that 67¢ savings will be the deciding factor.
Anyway, I think a subscription requires more thinking than a one-time purchase. You have to guess the failure rate, and then time replacements to arrive sometime shortly before your existing clothes fail. You have to receive an email and respond to it before your replacement ships, then you have to remember to collect the package.
Compare this to Amazon where you order two years worth of clothing at once, pay $20 to have it shipped overnight, and forget about clothes until they seem to be wearing out.
just sayin'.
regardless, though, you're right, its about convenience and margins. i've not done the legwork, so i don't know what the margins look like on something like this.