Imagine, coming home from work one evening. Tonight is the big Uldaar raid, and you are next in line for a tier drop. You log onto World of Warcraft, enter your account information, and then you see it...
You have entered an invalid password.
No worries, you just entered the wrong password. So you try the real password, but you get the same error message. You then begin going through any passwords that you have used over the years with no avail. You want to contact Blizzard to inform them of the issue, but you can't. You hired a power leveling service to level your character.
World of Warcraft's terms of service states that you are not allowed to share your account with anyone. In general, they do not go around looking for this. They know many players will often play from separate locations, so it is really hard to track. But, they are not shy about enforcing this rule if they find out you are breaking it. Simply by reporting your account as stolen can flag your account as a problem account.
Since you cannot report this problem without losing any of your hard work on your other characters, you sit and wait, hoping they change the password back. The best you can hope for is to get your account back, stripped of any gold and high level characters. All the gear and trade items you had saved up will have been sold and traded to another account for sale, leaving you with nothing.
All this because you wanted another high level character to play, but didn't want to spend your precious time leveling on your own.