What was the purpose of setting the movie in the 80s?

I honestly don't know, haven't watched the movie but I noticed there's a trend for movie settings being a decade or two in the past for nostalgic reasons and to have more style I guess. Sometimes the director or script writer grew up in that time so they do it as a nod to their nostalgic childhood.

It was done before the 80's nostalgia fad we see today. At the time, it was a new idea to make fun of the 80's era. It also allowed Sandler to justify using nothing but 80's music. If it was set in the 90's, there would be 80's music, but then there would need to be reference ace of base, chumbawumba, nirvana, Celine Dion, smashmout. and Aerosmith. All the other SNL projects were doing that, so this was just a way for the movie to stand out.

I liked this movie but in no way did it feel like the 80's

Let's see... why set this in the 80s? Because the 90s turned out to be a spastic ADD of culture. Don't get me wrong, I thought there were some fun moments back then but grunge came and went within two years, because all of the idiot "stars" at the time couldn't keep heroin needles out of their arms, the post grunge stuff was.... meh, then there was fucking rap-metal, then there was a disco resurgence, then there was Eurodance and Euro/Techno, then there was the latino music explosion, then there was the boy-bands and Brittney... right around 1998 there was this need to say, "remember when?" and the love for 80's came roaring back. 80s music in the early to mid-90s wasn't getting a whole lotta love, but that suddenly changed - and I am not implying that this movie singlehandedly did it, but it's fair to say it was a part of it.

At a time where there was no real identity, it seemed like this got made at the perfect time. When my friends and I discuss 90s music, rarely does Brittney, or the Backstreet Boys or Ricky Martin get brought up, it's always Soundgarden, Fuel, Alice in Chains... Even though the genres are wildly apart, it's easy to say Poison, The Thompson Twins, Adam Ant, Metallica and even older icons like Tina Turner and Bruce Springsteen are identified as "80s artists".

So it would be awesome