Even if you have a credit limit you could shop for more. I dont know where the limit goes but I passed my credit limit once and then had to pay a penalty fee. It felt a bit stupid to pay this fee since I knew that they had earned more money due to it... Greedy *****.

Btw, maybe the CC company want you to have a higher limit. I doubt that they find a big different between 5 000 and 10 000. If you only apply for 5000 and have to do it in a special way, they might not think its worth the hassle.