Why does the login page look different?
University services make use of authentication in many different ways, ranging from the simple and straightforward to the technically complex. As such, you will see changes gradually starting in Fall 2019 with the expectation that all services be transitioned by Winter 2020.
Since these are completely different authentication systems, they do not know about your authentication session, so when you switch from a service using one authentication system to a service using another authentication service, you will be asked to sign in again.
Here is an example of the old sign on page. This sign on page is used by both UTLogin and UT Shibboleth, albeit with minor differences.
Figure 1. UT Shibboleth Sign On Page
Here is an example of the new sign on page. This sign in page is used by Enterprise Authentication.
Figure 2. Enterprise Authentication Sign On Page
While you may have the most exposure to the sign on pages for UTLogin, UT Shibboleth, and Enterprise Authentication be aware that these aren't the only sign on pages used at the university. For technical reasons outside of the scope of this documentation, services which authenticate via Austin Active Directory (such as Office365) will all share a different sign on page. Others, still, may have their own custom sign on page (such as UT Lists).