could you add a html download on the page so that it can be installed from browser instead of needing itch app?
If format is the issue it wouldn't be just an html file, but instead a zip with the html and then the assets in their own folders inside.
Game size may be another possible reason why downloads aren't possible (itch . io has an approx 1-2 GB size limit.)
But I do see games with both options, so it is possible to have both.