The reason why Companies like Facebook or Reddit exist is because of the community, not because of a perfect, be-all-and-all interface.
There will always be a tailor made Reddit app that better suits a certain user-type instead of another, and if this can be made relatively easy from another app it makes no sense for Reddit to give basically free usage of its core asset, the community, to somebody that doesn't have to maintain the whole infrastructure and can happily offer an alternative for a fraction of the price, without i.e. having to put ads etc.