Don't be so patronizing. Of course they understand it, but what they want is something different from what you want: status in the demo scene. If they open source it they're likely to end up as a footnote in their own projects rather than basking on difficult-to-scale peaks among their peers.
It's not like open-sourcing it is going to enrich them in some more concrete fashion than social currency; in fact, authors of very popular open-source projects regularly find themselves in the humiliating position of having to beg for money.
...and since the demoscene is closely associated with the cracking/warez scene, the implicit message is always "if you want to know how it works, get a disassembler and figure it out yourself."
What? This doesn't happen.
The D programming language also had this problem for a long time (closed-source/non-Free compiler backend), but thankfully no longer.
That D's licensing issues are now gone, certainly benefits D.
Even if adoption isn't the goal, making it FOSS might still make good sense. Suppose the goals are novelty and technical achievement. More interest means more support in developing their novelty OS, no?