nazz
Doubting Thomas
There would be a real reluctance to leave the Law since a Jew is brought up in that tradition, but there already had been groups that we now call "liberal Pharisees" that tended to be more Hellenized and more inclusive, thus more emphasizing the "law of love", as it came to be called later. To me, Jesus and Paul are not saying the Law is bad and must be left, but that something was greater than the Law in their opinion, namely Jesus. Therefore, the following of the Law could at least be tolerated as long as Jesus' basic teachings were followed. Thus we see references to following the Law that appear to be inconsistent but really aren't. At least that's how I connect the dots-- correctly or not.
We have to remember that James is Jesus' brother, and we well know that hiding things from your brother ain't gonna be that easy. IOW, your brother is going to see you at what you really are, although maybe a bit on the negative side. Paul doesn't know Jesus that way, therefore he's probably unaware that Jesus squeezes the toothpaste tube from the middle and periodically farts. Therefore, it's not really hard to imagine why James is more going to focus in on the Law whereas Paul is more going to focus in on the more pristine image of Jesus.
It has puzzled me how it was that Paul, who never met Jesus in the flesh, seemed to have captured the spirit of Jesus' teaching better than those who walked with Jesus in person. I think as you say James and the others were too steeped in religious tradition and were reluctant to let it all go. It was probably much easier for Paul a Hellenistic Jew to adopt a more universalist outlook.