Why did PGA Tour golfer stop playing in middle of final hole Sunday?

Aaron Rai won his first PGA Tour title on Sunday, claiming a two-stroke win at the Wyndham Championship.
But the tournament didn’t officially end as darkness fell on Sedgefield Country Club in Greensboro, North Carolina.
That’s because Matt Kuchar bizarrely stopped playing after hitting his tee shot on the 18th hole, opting to mark his ball in the pine straw 212 yards from the hole and walk the course with the other players in the last group as they completed their rounds.
“It has been a really bizarre sequence of events,” said CBS Sports analyst Trevor Immelman as the network’s broadcast came to a close.  
Kuchar led the tournament after 36 holes, but was out of contention at 11-under when he stepped to the 18th tee to conclude a marathon, 36-hole day stemming from weather delays due to Tropical Storm Debby.
With the sun already set and visibility declining, tournament officials informed Kuchar, Chad Ramey and Max Greyserman that rather than blow the horn to suspend play, they would be allowed to finish the hole then or complete it the next day.
In an apparent attempt to finish quickly, Kuchar unknowingly hit into the group ahead of him, one that included Rai – who led Greyserman by one stroke at the time.
“Why did he tee off on 18 when the fairway wasn’t clear? To me that was the egregious error,” Golf Channel’s Paige Mackenzie later said. “It was completely disrespectful.”
After Kuchar’s ball landed left of the fairway, he informed officials he would finish his round Monday morning – even though he had no chance of advancing to the PGA Tour’s playoffs. As things turned out, Rai birdied the final hole to push his lead to two strokes and Greyserman closed with a par to finish second.
As the sun rose again on Monday, Kuchar was the only player back out on the course to make the results official.
He hit his second shot on the green and parred the hole to finish in a tie for 12th, earning him $134,695.
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