Hello,
Because HikaShop will send an email to the guest account for its order (and also a link to access to the invoice and links to download files, if they are some) ; that information is a requirement.
If you want to remove it, it would require to customize HikaShop and modify some parts of the core.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.