The title of this post is a little misleading. Music is not easy. Playing live takes incredible effort to even be in a bad band. Being even occasionally compelling on stage takes "10,000 hours" of experience and talent. Having any staying power takes organization, dedication and hard work.
Recording is half art and half science. It takes a great engineer AND a relaxed artist to make something come alive in a studio.
And songwriting itself DOES take dedication. I've been in bands where musicians say "I've got an idea for a song" and they literally just have two notes, a beat, or a quarter of a riff. And lyrically, an unfortunate majority of songs are glorified journal entries. Writing a good song requires an artistic mind starting with a blank page and solving a puzzle.
All of that said, how many pieces of great art in other fields have been created in under 30 minutes?
Vs. Other Disciplines
The effort-to-acclaim ratio is so much friendlier in writing a song than writing a novel that it's almost offensive; and I say that as a songwriter.
Yes, a songwriter still needs a great performance for the song to ultimately mean anything - but that performance can come from one person at home (e.g. Elliot Smith). How many people all working at the highest levels does it take to pull off a movie? A stage play? An opera? A symphony?
Even the solitary arts like standup comedy take dozens of daunting performances in unforgiving clubs to hone even one joke.
Keith Carradine & Nashville
Woody Guthrie used to believe that everybody should write their own songs. I tend to agree with him. We all have the potential. Pretty much every human is an expert in music based on listening to it their whole life (just like most of us are experts at consuming television). Under the write circumstances, anybody CAN write a song.
One of my favorite examples of the randomness of songwriting greatness is actor Keith Carradine winning the Oscar for Best Original Song in 1975 for "I'm Easy". The movie Nashville was a great Robert Altman satire about country and gospel music. The movie almost defines "sprawling" as a multi-character and multi-plot genre.
Altman was a famously collaborative director, he accepted input from anybody on set about anything. And he felt that way about music. His son wrote the lyrics to "Suicide Is Painless" from his M*A*S*H movie and between that and its use as the tv show's theme song, the son made more money off that than his father ever did for a movie. Altman also had many of the actors of the movie "Nashville" write the songs that they would be performing.
This includes Keith Carradine who wrote "I'm Easy" for the film. While Carradine had already been musical and likely played in high school, at the time he was solely acting and not performing as a musician. Lo and behold, he wrote "I'm Easy" which for a couple of hours of effort, goes on to win the Academy Award for Best Song.
One Hit Wonders
How many one-off "one hit wonders" happen in other creative fields? Not a lot of people have one great opera in them. Look at this great list of first-time film directors - Not a lot in the bunch who just flamed out.
But pop music history is littered with one-hit wonders, bands that put it all together for one short moment - and probably was helped by the era of some talented A&R executives whose job it was to keep their ears out for a great song, as opposed to the more turnkey modern approach of just seeing if a band already has a large number of social media followers BEFORE signing them.
For the record, when people like to make fun of one-hit wonders like The Vapors, Norman Greenbaum, The Troggs, Dexy's Midnight Runners, The Starland Vocal Band, etc. it seems catty and ridiculous. To get to the top of the charts even once is a huge accomplishment that may have had luck but that luck was always paired with hard work. And a musician can make a nice career off of playing summer festivals and placing that hit song in films.
People making fun of one-hit wonders remind me of jackasses at an NBA game making fun of the last guy on the bench. That 15th man is so much better at what they do than anything that loudmouth fan has ever accomplished in their life. End of soapbox.