Why do rates change with each company?

Because each company has a different target market for bikers, they will price their insurance accordingly. For instance, the safer rider will often be older and more experienced so if the company is looking to have safe, low risk riders then they'll price the younger rider out of the market.

The best thing to do is to look at as many prices as possible and then look into what's included (or not!) in the policy – you might find some surprises!