People don't really like grease. They use paper napkins to blot it off pizza, get angry if it stains their t-shirt, and scrub to get the scent of deep-fat fryers out of their hair after a shift flipping burgers.
But Grease—capitalized and italicized—is beloved by people of all ages and all generations.
Teens love it: Glee devoted an entire episode to it (the somewhat unappetizingly named Glease.) Old fogies love it: John Travolta and Olivia Newton-John reunited to sing, "You're the One That I Want" in 2012. (Source)
And everyone in between loves it: pretty much everyone watched Fox's Grease Live! in 2016. (Source) Starring Julianne Hough as Sandy and Carly Rae Jepsen as Frenchy, the TV adaptation was an insane hit.
Grease still lives on stage, too. A version of the musical seems to always be in production somewhere in the U.S. or U.K. And one of the writers of Grease the musical, Jim Jacobs, even revived his original vision: Grease set in a Chicago and much rougher and raunchier than the Broadway version and the movie it inspired. (Source)
Basically: as long as there are high school seniors hoping for a graduation that includes a private amusement park (good graduation, or best graduation?), Grease will be the one that we want.