Twitter is a powerful business instrument. In Eastern part of the world and Europe Twitter is not that much popular, but in States a lot of business is involved in it. Companies use twitter for free for their commercial purposes. Elon Musk plan to oblige them to pay for this instrument. I find it that simple. There is nothing to do with dogecoin or cryptocurrency at all. Regular users will continue to use it for free, as he promised. But companies will have to share their income now.
Indeed twitter is a very powerful advertising platform for tons of businesses and projects out there be it crypto related or not(although at the moment I see crypto and NFTs taking over the majority of traffic there). And yes, Elon never announced anything yet about utilizing doge on anything related to twitter. I reckon he may even create a new token for twitter to utilize for itself. I wonder though what will be his basis on measuring which businesses or individuals need to pay some "tax" of some sort and which are the ones that don't have to.