Looking at the instructions, it appears to require use of a gmail account only. Is it possible to use an existing, non-gmail account?
The reason for the Google login is to avoid any problems associated with retaining user credentials.
Hackers cannot access login information if the data is not located on the servers utilized by TroveStar.
While it would be fairly easy for a hacker to gain access to login credentials from an unprotected, user computer or device, gaining unauthorized access to Goggle's servers is a completely different matter.