The Force Awakens (SPOILERS)

[Sephiroth]

Because Windu is the best lightsabre duelist, not force user in general. Also I do not know if you have noticed but Sidious has played his little game in the entire scene to wait for a good moment. Also you have pretty much taken a bad example because with puni Jedi I did not mean the creme de la creme. And even those - I mean, Yoda tried it. And he failed. Hell, he even owned the Jedi in Clone Wars when he tested something (well, he considered it theoretically a failure but you can watch the battle yourself also he does other incredible stuff in Clone Wars).