Depending on the user scenario, the copy/paste alert can last seemingly much longer than 2 seconds as it can prompt multiple copy alerts - creating a continuous cycle of alerts.
For example, if any text has been copied, and you interact with the search/address bar in a browser (let’s say Chrome), the “Chrome pasted from x” alert will continually keep appearing every time you click on the search/address bar - OVERLAYING the search/address bar, so you are forced to wait for the alert to go away. This is a problem because of the position of the search/address bar and the copy alert (both fixed at the top of the screen).
Replicate issue:
Copy some text from an app (non-browser)
“Chrome pasted from x” alert displays for 2 seconds
Open/switch to a browser app
“Chrome pasted from x” alert displays for 2 seconds
Click on the search/address bar
“Chrome pasted from x” alert displays for 2 seconds
Click again on the search/address bar so that the paste option displays (this is hit an miss depending on how you tap the search/address bar before the alert displays)
Paste text in search/address bar
“Chrome pasted from x” alert displays for 2 seconds
I have now seen the SAME text alert multiple times over 8 seconds, just to complete a simple task of wanting to search for text in the search/address bar.
The alert will keep displaying until the text is pasted.
This now changes the expected interaction of the search/address bar.
Do you expect an alert to pop up to every time you interact with the search/address bar? Essentially disabling its access for 2 seconds? I doubt many users would see this as beneficial.
And this is why usability user research that includes many different scenarios is conducted, so that informed decisions about interface changes are made - not just done because someone said it was a good idea.