What you say is all true! In fact, I've always made demos available. Unfortunately, they were demos that could not include many of the game levels of the version of the game on sale, otherwise it wouldn't have made sense to sell it.
On the other hand, making the demo too complete gives the same result.
Two of these things happened to me:
- A: many downloads of the demos - few sales: the demo was unable to give a good idea of the game.
- B: many downloads of the demos - few sales: the demo was too complete.
Now I've removed all the demos from the ultra-tested games that I selling.
However, it is likely that my games are not in step with the times, that the graphics, in comparison with that of the other games, are poor, that the music is obsolete ... But everyone has his own style and there are those who do not like to change it, albeit going against the tide, at the expense of the success it will have. Doing everything yourself "is suicide" ... it is good to have at least personal satisfaction as an alternative to profit: the fact that you still have someone who is interested in what you have done, thus making the demos always available.