My interpretation is slightly different. They don't line it because of the commitment it creates.
1) From a legal perspective, it's only a matter of time before someone says, "You sold me this book. What do you mean I can't access it any more? I want my money back." What call action lawyer wouldn't love that opportunity?
2) The upfront cost of the ebook might be cheaper, but again, there's the ongoing infrastructure, etc. Those costs over time add up. Vs print the book once and be done with it.