Someone being "hard to buy for" isn't a reflection of how well you know them (or if you don't know them). It is simply a reflection of not quite being able to buy them some of the things they'd really enjoy. It is hard to buy art supplies for the artist if you don't make art yourself, and it is similarly difficult to buy an avid reader books since you don't know what books they've read. On top of it all, they might not need or want much - or simply not express the wants well.
My family has always created wishlists to address this, but now that we're all adults, we've got the issue that we can buy what we want for ourselves. I've had to make a policy of delaying non-urgent purchases and putting them on my wishlist instead, because otherwise the answer to "What do you want for Christmas?" is "I don't know—I already bought all the [reasonably priced] things I want!"
If Christmas weren't a thing, I'd've bought some new cycling gloves a month or two ago, but as it is, I'll keep riding with my very-torn-up pair until Christmas so my family can continue to partake in the gift giving ritual we enjoy without having to resort to finding random stuff the recipient probably doesn't actually want.
The curse of having enough money and not wanting a lot of things. :-)
