http://www.avclub.com/articles/why-are-most-sitcom-pilots-not-very-funny,62935/

Whether they fizzle out or thrive, TV comedies’ pilots rarely feature their finest half-hour. Why?

Because sitcoms are all about characters, and no one - including the people making the show - really know the characters yet in the pilot. Drama is more plot-focused, so a pilot usually works well as almost like the beginning of a movie. That's not how sitcoms work, though.

Plus, introducing your premise and your characters and telling a compelling story and writing funny jokes is a damn near impossible task. That's why when I watch a sitcom pilot, I'm not expecting to be blown away, I just want to see potential for the future. Community's pilot is one of my favorite recent sitcom pilots, but it's far from perfect - it just set a very clear goal of what the show wanted to be.

I agree. There is so much background information that needs to be established in a pilot episode that there isn't much opportunity for humor. Plus neither the actors nor the audience are yet familiar with the characters or the plot which also limits the comic possibilities.

10 Terrible TV Pilots That Led To Otherwise Great Shows (http://whatculture.com/tv/10-terrible-tv-pilots-that-led-to-otherwise-great-shows.php)

...The Arrested Development and Modern Family pilots were terrible? Lol, AD's is probably the fullest-formed sitcom pilot ever made, and Modern Family's pilot was fantastic, hence why it became a hit so quickly.

Then again, the criticisms of these are dumb. "The shows hadn't settled yet". Duh. What show has in its pilot episode? Rarely is a pilot is a great episode of television (though honestly, AD and MF are close) but there are pilots that are great because of the promise they show.

I didn't t care for family ties pilot

Because sitcoms are all about characters, and no one - including the people making the show - really know the characters yet in the pilot. Drama is more plot-focused, so a pilot usually works well as almost like the beginning of a movie. That's not how sitcoms work, though.

Plus, introducing your premise and your characters and telling a compelling story and writing funny jokes is a damn near impossible task. That's why when I watch a sitcom pilot, I'm not expecting to be blown away, I just want to see potential for the future. Community's pilot is one of my favorite recent sitcom pilots, but it's far from perfect - it just set a very clear goal of what the show wanted to be.
I was totally going to answer this but you beat me to it with your fancy fresh, well thought out words. God dammit, Joe.

Me and Joe have both written sitcom pilots. It's hard to accomplish everything you need to accomplish and still be, well, funny. If a pilot manages to introduce who its characters are, the central theme/plot of the show, and the direction it intends on going, then it's achieving genius levels of work.

http://www.pajiba.com/seriously_random_lists/the-best-comedy-pilots-of-all-time.php

Most sitcoms grow into themselves over a few episodes. This is normal, and not a bad thing at all, but it means that those comedies who come to life fully formed are that much more special. Additionally, the stakes are usually lower on comedies than dramas, especially in the pilots. (“Discovering your fiance’s corpse and finding out your dad is a spy” isn’t quite the same as “Getting a new roommate.”) Yet a good comedy pilot can still find meaning and humor in the little things, and it can serve as a hint of what’s to come. The comedies below all managed to debut as their true selves, and though they’d grow over time (as all series do), their pilot episodes are still fantastic summations of what the series wanted to be.