I ask this because it was
The highest grossing film of 1985, Back to the Future launched one of the most successful franchises in Universal's history, including two theatrical sequels, an animated television series, a theme park ride, toys, comic books, video games and apparel. http://www.backtothefuture.com/movies
Following a year-long grassroots effort initiated by this site, the U.S. Library of Congress announced in December 2007 the preservation of the original Back to the Future film by its addition to the National Film Registry.
In other words it was immensely popular. And the last one was made in 1990. That is just about the timeframe where Hollywood goes and starts making remakes or sequels to milk the cow more. Furthermore, you might get a cameo out of Fox or Lloyd before it's too late.
What is the current state of any plans for the franchise?