Honestly I think this is kind of it. Midweek magic to show modes of play people don't usually play and frankly standard fits that definition for a lot of players.
Oh hey, I was coming to say basically this.
We choose Midweek Magic formats for a variety of reasons. Sometimes it's novelty, and sometimes it's to put focus on a particular format. Players on this subreddit are among the game's most invested, and therefore the most likely to be a little weary of our evergreen offerings. I sympathize, but there are lots of other players who appreciate a little incentive to try something they usually don't, especially when the format has recently changed.
And even on the other hand, MWM being a format that you already play means that you already have decks ready for it. Variant constructed formats see less participation because of the friction of having to build a deck. For players who are already familiar with the format - who are already prepared and even may get to have an advantage from their expertise - a week where you already know the ropes can be an upside.