I stumbled upon this post in the Power BI Community because a customer had the same request. When they exported out of the Matrix visual they were getting tabbed data.
The csv file ends up being tabbed and the user wanted it to export just as it displayed in Power BI.
My solution for the problem was to create separate measure for each column. Then, I put the measures with the group in a table visual. This allowed me to export the data as the customer had hoped for. I made a demo video here: