Main driver for keeping engines private?

Ron“s list shows how many private engines there are. In addition there are many others, the latest versions of which have not been released for a long time (Jonny, The Baron, Quark, Petir, ...).
It is of course a personal decision, but I wonder what is the main driver for keeping engines private. Is it competition? Or lack of interest by the public? Or ...
Robert
It is of course a personal decision, but I wonder what is the main driver for keeping engines private. Is it competition? Or lack of interest by the public? Or ...
Robert