User blog comment:LordWeirdo/(Spoiler-free) Concise opinion of TFA/@comment-25595629-20160201173359

The absence of both Jedi and actual* Sith is the reason that no one was good with Lightsabers. Stormtroopers were trained to fight with sword-like weapons, sure, but the Jedi Order has been extinct for around 50 years. Luke and Vader were the last "major" Jedi and Sith, and while there were Inquisitors and rare survivors, Lightsabers were no longer a major force in the galaxy.

Kylo Ren's Lightsaber is a poorly constructed Crossguard Saber from Malachor. He swings his sword like a fanboy who grew up idolizing Darth Vader, simply because Vader wasn't alive to teach him. He had some training from Luke, but Luke himself didn't have many years of training.

Finn was a Stormtrooper and learned that the Jedi were enemies of the Empire. This means he was likely taught that Jedi would use Lightsabers to impale people and cause burn marks, rather than parry blasters. This is why he had little experience with using his Lightsaber to actively block Lightsaber/stun staff swings.

As for Rey...well, the Force works in mysterious ways.


 * Supreme Leader Snoke is not confirmed as a Sith, and he in fact displays Tarkin-esque opinions of how the Empire was run by Darth Sidious.