Because it is quite unnecessary to restart the computer just to fix Messages app notifications to correctly display contacts' name. Restarting computer is also disruptive when working.
Can you please be more crystal clear? Or show screenshots? Where are you opening contacts? Contacts app that is a separate app from Messages or contact information when you click on their name to open a popup menu or the details button in Messages app?
Where is this toggle button?
👍 Restarting the Mac is a PITA
Yes not clear about what toggle means LOL, I would be careful about turning a contact off and back on - you can loose the history of the text messages like this - fine if you don't care about the history - but I keep these for reference since many of my text messages are work related and have lost years of history for a contact when changing phone numbers in the contacts
I had to upgrade my storage because imessage storage was more than the 5g of free space - this can be an issue
Sometimes it helps to close iMessages and reopen - this helps ( for me) to restore missing messages and images, links etc.