system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why are most songs about three to five minutes long, and movies about two hours long?

Was this standard determined by commercial success?  Is it a matter of artistic expression?  Also, is there some threshold at which the average person can remain engaged through a song vs the same for a movie?
gpt
In the good old age before Commercial Radio songs were a multiple of lengths. Take for example Meat Loaf's bat out of hell or Queen's Bohemian Rapsody which are long. 

Commercial Radio required adverts to be inserted at specific points as the time was "sold" to investors. This meant radio required songs to fit a new rota system. In response recording companies had songwriters fit Radio Edit song lengths. That's why you will see Bat out of Hell Radio Edit which sort of just stops and rarely hear Pink Floyd tracks on radio.