SR1 was a criminal enterprise as well, and there's no indication DPR was stealing from his users. Trust is at least as valuable in the criminal world as it is in legitimate enterprise, if not more so. A criminal who runs a trustworthy criminal enterprise is likelier to do well in the long run than one who rips off his customers.
Allegedly, SR2 was setup in ways which made it much, much easier to run off with larger quantities of money than with SR1. Given the circumstances, you could reasonably conclude this would happen.
Running off with the money is probably the smart move. The quicker you can get off the radar with something like this, the better your chance of not ending up in jail. It is entirely possible they are made for life, and with no more incoming transactions, if they haven't left a trail, they can have their cake and eat it too.
But there was indications that DPR was murdering people who got in his way. Hardly an "ethical upcheck" here, and if he didn't steal from his users it was only because he didn't feel it necessary, not because he felt ethically bound for that.
In fact ensuring the ideal of SR paying out fairly would allow his business to grow and therefore his lack of theft could easily be entirely and completely pragmatic without needing a shred of ethics to support it.
You can easily throw that trust away and profit some bitcoins if your face is unknown. In the real world someone would come after you sooner or later. In the world SR1/SR2, Bitcoins and Tor? Only if the NSA has an interest.