Let me spend money on allies

I'm going to guess that the biggest concern here is hacked accounts.  If someone hacks your account, makes theirs an "ally" then spends the money on that account, they have to chase down someone through that.  Along with "I don't remember doing that, I only gave my password to 3 people on the internet!" complaints to customer service.  (And EA customer service is not only useless but a hindrance at this point)

At least if it's within your guild, there's less likely chance to get hacked and use your account to spend money on other accounts.