Why does tree work pay so bad in comparison to other trades?

[Andymacp]

Also large companies may have 4/5 teams out so can go cheaper on each job and still rake it in.

[Taupotreeman]

Having worked for a very large firm I can tell you that, with contract work, large portions of time can be written of to those contracts so that private work can be quoted cheaper e.g. You price a private job for a couple of hours knowing full well you're going to be there at least six. The remaining hours/time that you work over are written off to a large contract where it will be "lost".