The green "trolley" bus used for LAXit are brand new and they have luggage hold in the middle of the bus so you board using the rear door if you have large suitcase, and board using front door if you have only carry on. They also have onboard WiFi so you can use that to call Uber if you are foreign visitor and don't want to incur data roaming charges. LAWA ordered 50 of these buses and only 33 have been delivered so far.
LAWA also contracted with 3rd party operators to provide temporary and overflow capacity. And these buses are generally retired city bus and they may not have the proper setup for airport shuttle. And of course these old buses don't have WiFi. As the new green trolley buses are delivered, these ancient city buses should go away.