It used to be available on a donation basis, but some users are under the misconception that software grows on trees. It would be nice if it did, but it just doesn't.
I am very aware of the fact that writing, documenting, and maintaining software is a very time-consuming task. Add to that things like bug-tracking, reproducing errors (that's the worst bit), changes brought on by operating system vendors, and user support, and you find yourself in a seemingly never- ending cycle.
I do a bit of programming myself, though little of that is for public consumption. (Most of the code I create is dropped into a customer's tool-set, and never leaves those premises.) The one minuscule "public" project I've published in the near past is whatmon, an extension for Mozilla's Firefox and Thunderbird offerings. I mention this only because it proves a small point: it is time consuming and sometimes a pain to maintain even that tiny program for every jump in version number and API change that the Mozilla Foundation imposes on their products.
I often rave (in public) about good software, programs, systems, and tools created by clever and laborious people who often provide the fruit of their work free of charge, and invest a large portion of their time in maintaining them. Anybody who reads these pages regularly knows that.
Developers will develop, but users should reward developers in turn.
I hate software that doesn't work reliably, particularly if I have to pay for it, and I love good software, particularly if it is free of charge. (The best of course is Open Source.) I buy software (and I pay for it myself -- I'm not backed by anybody) if it is worth it. Small programs such as MarsEdit, NetnewsWire (yep, I paid for it before it became free), larger ones like VMware Fusion or PGP WDE, as well as huge ones like Mac OS X itself, just to name a few.
If I decide to continue using ABxLDAP, it will be because the program does what I expect of it and does so consistently and reliably, and for no other reason. If that happens, rest assured: I will pay for it, because software doesn't grow on trees.