Can't buy 2 copies of Diablo II (or other games)

I just tried to purchase 2nd copy of Diablo II via the Blizzard website, but it won’t let me do that, saying that I already own that game. Apparently, the only way to get a 2nd copy is to set up a different account, using a different e-mail address??

This seems like a rather bizarre restriction, given that parents may want to purchase multiple copies so they can play with their children.

You can only have one copy of Diablo 2 per Battlenet account. If you wish to have your children play you can do that though. To buy D2 2000 or LoD 2001 for them you can buy it as a gift. Click the Gift button and you can have Blizz send it via email to them or you can have the email sent to you instead and you personally set it all up for them.

Ideally you want to set up a second Bnet account in your name for each minor child. That requires a separate email address for each account. You can also set up Parental Controls to prevent digital purchases, control play time, get play time logs, and even control chat options for modern games.

Now that they have their own Bnet account in the parent’s name you are set until they are 18 at which time you contact Blizz and have it transferred to their name.

https://us.shop.battle.net/en-us/product/diablo-ii

I just tried to buy D2 for my daughter, I set up her account such that I’m her guardian, but it wouldn’t let me purchase it for them as a gift until I added them as a friend. Now it tells me I haven’t been friends with her long enough and have to wait 3 days??