Why is prana-pratistha not performed for the utsava-murtis though they ave their own names?
The very word pratistha means lay in a solid foundation, that is, fix firmly on the ground.
So prana-pratisthita Deities are by definition non-movable except for emergencies – so Deities that are to be moved can’t have prana-pratistha done for them.
Prana-pratistha is not the only way to invoke divine presence eg. Naimittika Deity worship with Arohana and Tirobhava as in 10 day Ganesh puja or 9 day Durga puja
The essential thing for invoking the Lord’s presence as the Deity is not the prana-pratistha, but the request of the pure devotee – that’s done for the utsav murtis