Possibly because Oscar Hammerstein II was his mentor, I find that virtually all of the characters in Sondheim have their 'I want' song early in the evening. FORUM, NIGHT MUSIC, FOLLIES, COMPANY and on and on - MERRILY certainly. And in large part because Sondheim;s musicals are character driven.
But Kander & Ebb do it, Ahrens and Flaherty do it, Jerry Herman did it, Loesser, the list goes on and on.
And Hamilton (I learned last night that CAMELOT is one of his favorite musicals - the show that opens with a scene structured after the opening act of Verdi's DON CARLOS) - Alexander Hamilton, My Shot, The Story of Tonight, The Schuyler Sisters , Right Hand Man, You'll be back. All character defining 'I want' songs. Bang bang bang. At heart its a 1956 musical in structure - which is one of the subtle reasons it works so well.