Switching both the scanner and payment processor, and modifying all of our systems to use the new processor, would be non-trivial. We'll stick with what we have now.
As I mentioned, we're not the only site that does this. The banks I use also do it, as does UPS. It is a security precaution that makes some sense.
If you just set it up to stay logged in, you can avoid having to log back in entirely.