Solos are good, because they let our ear hear something different. Also, your groove doesn't change up all that much. Give us some variation. So, perhaps the trombone sings a little, and then maybe the clarinet cuts the trombone off, then maybe they fight a little back and forth. The two instruments make it interesting to listen to, because suddenly it's not the full sound of all the instruments, but only one sound. Then another, and a call and response--especially with very different instruments--is yet another thing, before we go back into the familiarity of the main part.
Many jazz songs will play for a while, focusing on the main melody and groove, then the sax takes over. The piano provides some chords, the drum a basic rhythm, but mostly, it's about the sax. Then the trumpet. Then the drums. Then the piano. And back into the groove with everyone. You see what I mean?
Static just means it kinda stays the same, and that can get boring, no matter how good the music is. Variation is good, and then bringing us home to something familiar is good, as well.
Just realized a lot of other people said basically the same thing I was trying to say, so let me offer this terrific example by Jason Robert Brown (and this makes the second post in five minutes that I've mentioned him!):
Im in Bizness - Putfile.com