Maybe you should communicate more along the way of a project? Sounds like they think you're happy doing what you're doing and then "you suddenly quit".

That is a good assessment of the situation :-)

If your communications with your teammates is poor enough that they are surprised when you quit, it's likely you're not getting good information about other aspects of the companies you denigrate. Communicate more openly, with more people to get a better understanding of what's going on.

Definitely try consulting. I've always been a consultant and get bored incredibly easily when programming for money. Regardless of how interesting a project is; we are still doing this for money. Benefit of consulting is that when the term ends be it 4 weeks or 4 months, onwards.