Spawn camping allows people to sit in one spot, do nothing, and get kills easily. It allows small groups of people to sit in one spot, do nothing, and rack up lots of kills. It's sort of like IRC, with artillery pieces.
Look at total kills per tour, Rich. Spawncamping is probably the single most popular activity, because it requires almost no skill- no SA, no complicated maneuvers, no extensive training required, no knowledge required of aircraft capabilities, weapon ranges, fuel states... it's vulching for the hopelessly inept.