I was thinking the other day (yes, sometimes I DO that)....
And I was remembering the great comedy acts of the past- Laurel & Hardy, Rowan & Martin, Martin & Lewis, Hope & Crosby, Cheech & Chong, Burns & Allen, Homer & Jethro, Marx Bros., McKenzie Brothers, Penn & Teller, Smothers Brothers, Stiller & Meara, Three Stooges, Wayne & Shuster, Firesign Theatre, Monty Python and who can forget Sacco & Vencetti?
Now, it seems that all the comedians are Solo. Maybe, like the Music scene, the comedy clubs can't afford to pay for two or more comedians in an act-- so everyone does solo standup.
Even in the music world, when you play the bars, the easiest way to cut your pay is to offer your performance as a duo or a band. You'll usually get less pay as a group than you would as a solo! I know it doesn't make sense but that's the reality. That's why you're not seeing as many groups playing in bars today.