Requiring a valid login before buying tickets is one of the ways we protect against credit card fraud. Thieves programmatically attack order forms exposed on the Internet to validate the numbers they've stolen. Businesses that don't take steps against credit card fraud put themselves at risk of being denied the privilege of accepting credit card payments. We appreciate your understanding!
You also benefit by having secure access to your order history, displaying the tickets in your mobile device instead of having to print, and so on.