Where are you getting this? I have seen this stated a number of times in multiple threads and couldn’t be bothered to correct it. This is false they had a second team working on this game to begin with then moved over the entire team after the release of the Witcher 3. I remember watching one of their conference in 2011 or 2012 of them talking about this. The game has been in production for a long long time with a greater focus placed on it after Witcher 3 release.
CD Projekt Red unveils Cyberpunk 2077 at E3 2018
"It's been over 2077 days since we announced our plan to develop Cyberpunk 2077. We released a CGI trailer, gave some interviews and... went dark. Normal procedure for these kinds of things - you announce a game and then shut up, roll up your sleeves, and go to work. We wanted to give you The Witcher 3 and both expansions first, which is why this period of staying silent was longer than we planned. Sorry for that.
"As soon as we concluded work on Blood and Wine, we were able to go on full speed ahead with CP2077's pre-production."