The Tirpitz was the Bismarcks sister ship, the Bismarck being released into the Atlantic one year before the St. Nazaire raid. This meant that the Bismarck still had a place to get repaired on the Atlantic side. So, it getting hit meant it could go to France and get repaired.
The Tirpitz while in the North Sea lost the only port big enough on the Atlantic side, to repair it, the St. Nazaire dockyard. If the Tirpitz was in the Atlantic and got damaged it had no where to be repaired except back in North Germany, or Norway that meant sailing through the Channel or over Scotland, both very hazardous.