That actually is a pretty bad argument. If you want to experiment and find out how things work and "learn new things" 3DGS probably is one of the worst pieces of software you could choose with "no source code" probably being the major flaw...

In order to learn how tech works etc. go for e.g. Ogre or Irrlicht to get a playground for free or buy something where you have access to the source code...

I hope you didn't want to point out that the behaviour described by Machinery_Frank is a downside because it actually saves every dev from reinventing the wheel in order to get some common effects...