I employ about 20 people.
About 70% of the time, when people quit my company without notice, they are leaving with business. A client talked them into contracting with them directly at a higher rate, or another company made them an offer based on walking with a project.
It's a free market and people are supposed to do what makes them happy and all, but shady is shady. I check people's references before making them an offer and never hire people who have left a job without notice. I don't take on projects people bring with them unless they have been away from their former employer for a long, long time. I am not making assumptions about someone's reasons for quitting without notice - in fact, I usually give people a chance to explain themselves, and I would be open to hearing reasonable explanations.
The thing is they never do. I hear a lot of grousing about how work was part of their last job, he / she "just couldn't take" some aspect about it any more, or how there was this bull and it had horns and those horns needed to be seized. But no one has ever pointed to legitimate factors such as an abusive workplace, not being paid on time, not receiving fair / just compensation, or the like.
(Well, to be honest, that's not true. There was one time that someone left a job in protest after management refused to put in assistive devices to help with his handicap. I could understand this. But he was not being honest about his experience and lost out on that factor.)
I don't know if I am the only employer who is like this, but I suspect there are more people who do things this way than you might expect. Seriously, I just want to know when I invest in training people up, having them travel the world with me, setting them up as a thought leader, listen endlessly to their stories about kids and dogs and things they want to buy and their colds and everything else, they are going to at least have the courtesy not to vanish on their way out.