MM does it as an "homage". Reading the history of the spelling can be entertaining. The break largely came when a few Irish producers decided to add the "e", but even then it wasn't 100% for some time after, and before that was spelled the same as Scotch whisky.
To be single malt Scotch whisky there are specific requirements. Beyond that - the joker is and has been wild, lol, but I think the Irish produced has uniformly had the "e" for a long time.
Thank goodness "milk" is uniform and we learned as kids that chocolate milk comes from brown cows!