Then in 1971 the two separate holidays were homogenized into one.

The act reduced two national holidays in February into one. One was less disruptive to Wall Street and cheaper. Back in the day, national holidays were paid holidays in most businesses. 

The act was coined to the public as "President's Day" as more equitable to all Presidents, rather than just two. For the most part the public bought, but, again there was that public voice dissenting to the degradation of the national holiday, it's meaning and celebration.

...the holiday (click here) became popularly known as Presidents’ Day after it was moved as part of 1971’s Uniform Monday Holiday Act, an attempt to create more three-day weekends for the nation’s workers. While several states still have individual holidays honoring the birthdays of Washington, Abraham Lincoln and other figures, Presidents’ Day is now popularly viewed as a day to celebrate all U.S. presidents past and present.