What is it?
From its README we can get to know, that it programming language that aims for c# like syntax with compilation to c with GObjects library.
When I saw the syntax of vala, I thought that it could be a great replacement for c# (truly unusable on linux).
It is mainly used for gnome environment development - for e.g. Elementary OS only uses vala for their app creation.
Why didn't I heard about vala before?
I think that it is mostly dependent on its inclusively for gnome app development and lack of available libraries. Its not that wast, offenly unclear and old documentation doesn't help with inviting new programers.
Because of those thinks there is a lack of development power which causes its unpopularity - closed circle ♾️