I'm pretty sure it was just a skill that was difficult to actually get powerful enough to block anything like a blaster bolt, seeing as nobody except Yoda ever used it during the clone wars show, which starts 1.5 years into the war. If it was a very simple skill to learn then everyone (or at the least everyone at the Jedi knight level and above) would have learned it. I mean I understand the logic of "well I have a lightsaber so why use my hands" but still disarmament happened and left Jedi helpless, so I don't think it was a easy skill to learn.