That's his question - why doesn't Android have it?
Keep in mind though, "Do not track" is almost meaningless. The website gets decide what it will do if it sees a "Do not track" header, and many just ignore it.
There was a chromium switch back in the days like --disk-cache-size="x bytes" it's what he means I suppose. Don't know if it still exists though or if chromium based browsers do have any limitation on the size.