I cannot explain why either, but I work for a Lennox dealer and they will NOT put in anything but OEM in the Pulse because it does not last.
I have been back on some that other companies have installed aftermarket motors in a sort time prior. The HO thinks the tech did not do something correct and that is why the new motor died so soon.
We just say it is wired correctly, as long as it is, and order the OEM motor and cap. Usually never have an issue unless it is a bad motor out of the box.