Because the project competes for attention with a million other OSS projects out there and lowering the barrier to entry for newcomers is good practice for projects that want to stay alive.
I certainly agree that it would be a good thing to do for their own sake, but also at the same there is an amount of effort required. If someone is so lazy and has such a low attention span that they can't even be bothered to find the tutorial before deleting it, were they really going to stick with it anyway? It seems like such a low bar. I honestly think people are just spoilt by these modern FOSS projects with insanely good documentation. You just can't expect that everywhere
Also, frankly, Pharo has its niche. It isn't really competing for attention in the same way as others, since it is the "goto big Smalltalk"
