|XP is just a number|
Let me address the physics first. To very high accuracy, any satellite will follow an elliptical orbit. There is no natural spiraling orbit that you can take advantage of. (Except for the spiraling caused by atmospheric drag.)
The spiraling effect that I was talking about is achieved by arranging that a satellite's orbit is going to get repeatedly boosted by tidal effects. So you aim it so that it gets one boost. You then make a very small adjustment so that the orbit will get another boost. And another small adjustment so that the orbit will get another boost. And so on. The energy needed for these adjustments is far less than the size of the boosts, so you manage to move the satellite from one orbit to another with far less input of energy than flying there directly. But aiming a satellite so that it gets a series of those boosts without readjusting is impossible. Generally each one leaves you not quite lined up for the next. And even if it might, aiming it precisely enough to actually hit a sequence of boosts is an act of precision far beyond our capability. (I would not be surprised if it requires knowing position and momentum below the limit of the Heisenberg Uncertainty Principle.)
Also I note, again, that if you get your garbage satellite to the junk, it is much simpler to just give your satellite a garbage can, and put the junk into it. The real cost here is the effort of maneuvering your garbage satellite.
Therefore this effect can be used to move a satellite to the space junk. (Albeit very slowly.) It can't be used to easily send the junk on a collision course to the Earth.
Now let's move on to economics. You're right that public goods can be provisioned in some special cases by public markets. As I pointed out in my first post (with examples), and as is discussed at great length in The Logic of Collective Action, public goods get provisioned by free markets when the benefits to some individual or small group of provisioning them outweigh the costs. (They also can get provisioned through organizations in a variety of ways, which inevitably involve some form of coercion. For details go read the book.)
Given the extremely low cost of distributing software, the cost threshold of providing software to the world is very low. It furthermore turns out that there is no shortage of potential returns for an individual that justify contributing. And the result is that the public good of open source software is provisioned amazingly well. All of this fits perfectly with the economic theory. In fact I remember noticing a passage in the book which describes this state of affairs and correctly says what would happen, but then goes on to say that it is extremely hard to imagine a public good where this would be true. (Do remember that this book was written back in the 1960s.)
However software is a very unusual case. And your experience with open source software should not mislead your intuition about the problem of space junk. That has far higher costs and far lower benefits to whoever deals with it, with very predictable consequences.
About the benefits of removing the junk. You claim that you've repeatedly pointed out that they are high (loss of satellite) and I've ignored you. That's a blatant lie and I'd like an apology. Please read Re^8: "Practices and Principles" to death and search for it is easier to just avoid stuff. Go to Re^10: "Practices and Principles" to death and search for Junk is individually easy to dodge. That makes this the third post in a row where I've pointed out that the real cost of any particular piece of space junk to any existing satellite is that the satellite might have to make a maneuver. Once. (The odds of any particular piece of junk and satellite having 2 potential collisions is ignorable.) Which is a capacity that all satellites have.
Let me emphasize the logical consequence. Since I've brought this point up multiple times, and its importance has not yet sunk in, I'm going to make it big and bold in the hope that this time it won't sail over your head.
No satellite operator will pay more to remove a specific piece of junk than the cost of maneuvering their satellite out of its way. Which is orders of magnitude less than the cost of removing that piece of junk by any technique known to man.
Meaning that nobody will ever choose to remove that junk. And, of course, if nobody ever removes any piece of junk, then all of the junk stays there until it is removed by natural causes. Which usually means atmospheric drag - a process that generally takes centuries.