One might be okay, but you can't follow a show tune with anything. show tunes are out cause the audience is drained (in a good way!) from the last one, so it won't get the reaction it otherwise would. Anything other then a show tune is going to be lost.

So if one person is hoggin all the show tunes (you can only do so many in a night) it leaves every else unable to do one, and it make the next person unable to do anything and be noticed. (may as well play three verses of twinkle twinkle little star each time for all it matters)

Varity is the spice of life. Advanced tunes are NOT the only powerful ones. Many simple songs have great power. Most songs do not have exceptional power, and yet they are worth playing. Respect your fellows by doing a few of the show ones, but a lot of ones that make it possibale for others to play what they want.

I haven't played enough sessions to see this behavior, but I can imangine how it happens.