Papadopolus was spied on in London when just a new up and comming analyst with potential by 5 eyes (there seems to be no other reason than he seemed talented). Then was set up to meet some Russian officials and worked for Carson Team. After Carson dropped out he went to Trump team. Page has been a long time FBI and Russian stooge - Russians even called him a useful idiot. Manafort was just a dirty player like Podesta and had been for years. Cohen is another dirty player - was useful at a time but had no loyalty but to the almighty dollar.
All were used by 5 eyes and C_A for an agenda to make it look like DJT was in the pocket of the Russians. Add in the real Russian hacking of the DNC from 7/2015 to 7/2016, the successful phishing in March 2016 (Seth fits in there somewhere as well -DNC hit from at least 3 angles) and you have a narrative to pin on DJT.