Ruby chocolate is a type of chocolate, not a type of cocoa bean. Just like "white chocolate" is a specific combination of cocoa solids, cocoa fat, milk and sugar, milk chocolate is another combination of these, etc., so is ruby chocolate.
So, to your points:
Why does Ruby chocolate have virtually no fiber in it?
Because it has almost no cocoa solids. You say that it has "some" cocoa solids, but the actual amount is very low. It is actually quite comparable to colored white chocolate, but the ingredient which gives it its coloring and aroma is extracted from a specifically preprocessed cocoa bean of certain varieties ("ruby cocoa beans"), not synthesized.
Why does Ruby chocolate always contain milk in it
Because that's what ruby chocolate is. It is the specific combination of milk, preprocessed ruby beans, etc. If you were to make dark chocolate out of the same beans, it would be dark chocolate, not ruby chocolate.
What is the color of cocoa butter extracted from Ruby cocoa beans
I haven't seen it done, so I cannot tell you what it looks like, physically. The liquor they use will certainly be colored, but it is also theoretically possible that the cocoa butter has a pink tinge.
Why there isn't any Ruby cocoa powder available? I mean finely ground dry pink cocoa solids which are left after cocoa butter extraction.
This is a marketing question, not a cooking question. The producers haven't decided to market it that way, and we cannot know what factored in in their decision.