How many loops do you see, when you set the LoopBrowser to GarageBand? You may not have all loops installed, that come with Garageband.
I am seeing 1224 loops with the menu set to "GarageBand". How many are you seeing?
If there are many less, try the GarageBand menu "Restore Sound Library". you will need a fast internet connection, because that will download many GB of loops again.
Did you uninstall GarageBand '11, before you upgraded to GarageBand 10? Or is it a new Mac, that never has seen the older GarageBand versions?
It is hard to tell for me, which loops should be there, if you have clean install of only GarageBand 10. The green, software instrument loops are only in the GarageBand section of the Loop Browser. None of the newer sections "Hip Hop" etc. has software instrument loops. I may be seeing loops that migrated from GarageBand '11 in the GarageBand section.
If you have an older Mac or a backup of an older Mac with GarageBand '11, compare the loop libraries in the folder /Library/Audio/Apple Loops/
Then try to copy missing loops from the old Mac to the corresponding places on the new Mac.
If the software instrument loops were really missing in the new garageBand version, it would be a disaster. I mainly use software instrument loops, because it is easy to see which sequence of chords they will be playing and I can use them as a starting point for my own chord progressions. The real instrument loops are poorly documented. It is hard to tell which chords they will paly from looking at the cute names in the loop browser. It is wasteful to have to listen to a loop when browsing them.