Why Guillermo Vilas is not ATP Year-End NO. 1 in 1977? He won 16 singles titles w/ Roland Garros and US Open?

Answer 1

This is a nitpick, but the ATP Tour didn't officially come into
existence until 1990. The governing body for men's tennis prior to that was the Men's International Professional Tennis Council.
I'm guessing the points distribution is the reason why. The
tournaments Connors played in 1977 or were worth more on
average than the tournaments Vilas played in 1977, accounting for the discrepancy. World Tennis, the magazine of the sport at the time, gave Vilas the number one player for the year over Connors. #2 is the highest world ranking Guillermo Vilas acheived during his career, despite winning 16 titles in 1977, a record only matched by Rod Laver.

Answer 2

Jimmy Connors was the APT year-end No.1 in 1977, which he won since 1974 up to 1978. Though Vilas won most tittles in 1977 with 16, the points he received might be less than Connors...if he played in the lesser/smaller tournament which give lesser points than others.
Villas also leads in the win-loss leaders( most matches won in season) in 1977 with 131-15 and stood one in the longest streaks before 1990 with 46 in 1977.
So..be cool..he was great..

Answer 3

He might have lost in the 1st round of the other tournaments, or he might not have been able to defend the titles he had won the previous year. You lose just too many points if you fail to defend a title.