Why does TT require one user account for all installs?

This new requirement to use one user account for installing on up to 5 computers seems insane. The purchaser (me) of TT should not be required to share my login credentials with my kids so that they can do their tax returns.  Am I missing something here? This is a terrible way to handle security. Surely, there is a way for our family to use the "up to 5" returns as we have done in past years.