WarhammerTV is (a) cheap and (b) not GW’s main product.
The 9.99CAD is for WarhammerTV & Warhammer Vault & the exclusive miniature & unlimited army lists in the AoS/40k apps & a discount on merch.
The audience (i.e. people paying that money) is tiny compared to, say, Netflix.
So it isn’t bringing in a lot of money so GW isn’t motivated to spend a lot of money on making the app to view videos actually good.
They are a miniatures company who make most of their money from miniatures. They are keeping their focus there and most diversification is, I guess, usually one guy’s pet project rather than a major business move.