I'd rather call it "involuntary" monopoly.
It's just that no other team of qualified individuals out there (like the VAM team) exist to bring up a simulation program like VAM in the market.
What VAM does is way, WAY beyond anything else attempting to 'do this too'. But it's not "because of" VAM's existence. It's more because VAM's team did the right things at a good moment in time. I'm sure that other potential teams (that don't exist, yet) could maybe "compete" with VAM and come up with their own VR simulation stuff. But the momentum of VAM means that they'll have the upper hand because they had years of a head start.
I'd probably compare their situation they're in with where Valve positioned themselves in a specific market (digital distribution market) with Steam at the PERFECT moment in time, where basically there was 'nothing like it' even though other big companies did exist... but simply didn't think of doing it before Valve did (or didn't do it the same way, if anything).
VAM currently is on the high ground and have a head start. We've had years worth of content from the community built for it, too (which any other would-be VAM competitors would have to see happen as well, because the MODS for VAM is a major fuel and contributor to the very reason as to why people do use it or are at least curious to try it).
Maybe in 5 years from now, we'll see a solid VAM competitor either being made and we'll all witness it happening; or currently already exists but is nearly unknown but will grow into something much bigger in the next couple of years. On the other hand, it's not like VAM will 'stagnate' either. VAM 2.0 is coming, and with it, a LOT of extra potential on top of anything the current 1.x version can do (or rather, cannot).
If other individuals right now are seeing VAM and think "I'm sure I could do better" have the intention to give it a try then... well, they need to do that for a start. Because as of now there's just nothing on the level of what VAM can do. And it's not that VAM itself is perfect, or that it doesn't have limitations or issues, or that its User Interface is a plight for our eyes and our brain.
But despite the issues, on purely a technical level, nothing truly compares to VAM nonetheless (which I suppose IS the very impressive thing about it in the end, people and critics alike can say whatever they want "against" VAM, but they'd be hard-pressed to find anything else on the market of VR simulations at the moment that can do even half of what VAM does).
