Plus, lightsaber combat by the time of the OT had become a lost art. Palpatine no longer used his weapon and remained largely confined to his Imperial Palace on Coruscant studying the Dark Side, Vader was a cybernetic shell of his former self with slower reflexes encumbered by his mechanical parts, Obi-Wan had spent 20 years in the Tatooine desert not needing his own lightsaber for the most part and Luke was a green newbie who took four years to progress to the point where he could defeat his father in combat, and then only because of anger and hate that brought him perilously close to the Dark Side.
And Yoda? He had no need for his weapon as a little green refugee living on a murky swamp planet where the biggest threats were native flora and fauna.
When the Jedi Order had been erradicated and the two Sith Lords seized control of the galaxy the need for lightsaber combat had largely ceased to exist. By the time Obi-Wan duels his former apprentice for the final time aboard the Death Star in ANH he's a 61-year-old man who's spent two decades in exile without worthy opponents. He was going to be sluggish and exhibit deteriorated reflexes as he entered old age.