A Party Of Newbs

Why is it that starting level adventurer partys only have novices in them? Its like the masters of said novices tell them , " Go ahead and adventure now and dispite spending much time and money training you I won't go with you but hey you have got your other inexperienced novices to help you survive." Who says training ends at first level? I was thinking of old school Clerics who don't have any spells yet. Why would they go out adventuring alone? It seems more likely that a group starting to adventure would hire or otherwise get someone experienced to join them. So the next I'm Dm , a starting party will have a couple of higher level NPCs to" guide" them. Anyone else like this idea?