I think people have been trying to justify the act of language creation for as long as people have been deliberately constructing language. My own reasons are perhaps not significantly different from theirs.
As an inherently social phenomenon, language is never the property of one individual at a time. But a conlang, at least at its origin, may be considered private property. This is a very peculiar state indeed for language! Therefore, I think it is necessary to imagine an eventual collective of users for any constructed language.
The meaning one assigns to this work of language construction is, it seems, deeply personal. I wouldn’t presume to know what it means to anyone else but to me. And those reasons I will keep to myself for the time being.