Why is my credit score 675?

I am wanting to know why my credit score are not higher. I have 3 Credit Cards one with 300 limit other two 500 credit limit. I always pay them in full every month. i have never been late. I also have a student loan and its 2500$ on my report but its in good standing bc i dont have to pay on it until im done with school. I have a few inquiries bc i been trying to get a motorcycle loan but keep getting denied. I also have a secure loan with 500$ left to pay. I took a 1000 secure loan to buld credit. I been paying on the loan for 5 months and have about 5 more months left. i have had my CC for about 6-8 months on all of them. I know im just starting out with credit but i dont see why my score in not perfect. Sometimes i spend 80% of my credit limit sometimes i only spent 5%. I want to know why i cant get a good credit card with good APR and why i cant get a motorcycle loan. all they say is my credit is to limited. how long befor i wont be limited and have a good credit score so i can get better credit cards with higher credit limits.? thanks for you imput. i think i put all the info to help with ur answer.