You dont fucking get it. He doesnt need to pair them up or have them fuck, date or flirt. He only needs to suggest that there is a possibility for it, and that it may already be the case.
The same reason your dumb shipper ass argues for asukaxshinji right now is the same reason marixasuka shippers argue as well. The point is not to deliver a story, a romance or anything else. Only a framework for otaku to build their fantasies on.
You have taken the bait. Mari exists to add yuri fans to Asuka's fanbase. The Shinji hinting is to please existing asuka fans and bait hetero shippers.