This is because you and every one else don't understand the differents between a production company and Network. CW is a network who airs TV shows they only care about ratings. If show makes the grade they will keep it on there network. Studios are the ones who actually make the show. They care about making money that will keep the show on the network.
In short if a love triangle where to happen on Constantine it would have nothing to do with Network; it would all be on the studio who write and produce the show.
There are many shows on CW that don't have love triangles. The biggest one that doesn't have that at all is Supernatural. So Constantine could carry on the CW just as it is with no changes. The only difference is that it has much stronger chance of Surviving then on NBC.
It really doesn't matter any way. If the show gets cancelled the chances of it being moved any where will be so astronomically small it's not even worth talking about.
Also you think it will survive better on SyFy. Well let me be blunt it will have even less of a chance of Surviving. SyFy stopped being SyFY years ago. They don't play these types of shows for the most part and ones they do have are of poor quality and not worth watching. SyFy has become about reality shows and wrestling.
If Constantine where to be moved to SyFy it would slip fade away and die slowly. Most people wouldn't realize that it was still on the air. The ones that did would watch it but due to lack of money the production company would have to take short cuts and thus quality of show would get worse. This would eventually lead to viewers to stop watching and lead to the show being cancelled.
You want to know how I know this? It's because almost all the shows that aren't Reality or wrestling suck or have been cancelled. I rather see it die off then moved to SyFy. I used to live on SyFy channel and now I don't watch it because it stopped being the SyFy channel. They sold out and sold out people like me who loved SciFi shows.
Again it doesn't matter cause it will not be moved. More then likely it will be cancelled and that will be that.
IIRC, Syfy is trying to go back to its roots with some new shows lined up.