So first off, I get the frustration. 100%. One person's choice can and does have an impact on the other players/GM enjoyment. One player choosing not to make it - particularly for reasons you don't find personally compelling - is a pain in the butt. Your personal, recreation time is being negatively impacted by another person who theoretically wants to game with you but is making choices that do not seem to suggest that really is their preference. So it does seem like the best option is to encourage everyone to 'put a golden box' around those hours. It just doesn't work out that way in my experience.
First off, that turns you into a bad guy sooner or later. Seriously, at some point that player will want to be [X] and you will be putting pressure on them to make the choice you want them to make instead of the one they want to make. That works for bosses because you get paid for forgoing the thing you like to be where someone wants you to be. Or it works for relationships because there are a lot of other benefits to being in the relationship (you hope). But in social, recreational circumstances that doesn't work. Not on a long term basis. They are getting a lesser recreational experience when they wanted another experience. That's not a good return on investment for your social group. You are creating a situation where your game is a drag for at least one player. And that player often serves as a drag for everyone else. (Not always, of course, but it's hard to really bring a positive vibe when you are somewhere you don't really want to be.) OR... it's an empty requirement. And those are not productive. Telling your players to put the game in a protected time and then letting a player out (of attending, of experiencing consequences, whatever) for anything not genuinely acceptable (illness, emergency, etc.) just tells your other players you aren't really serious.
Which isn't to say that it's not sometimes a wise choice to let players know you take the game seriously. If this isn't their top entertainment priority, they should let you know so they don't join the game since they will eventually disappoint you. Or you gotta decide the game is such a priority for you that you are willing to do the work (suffer the disappointment at some regular frequency) to get the game. Those are really your only stable options. Drive people who aren't as committed as you away as you search for the perfect game. (And if you do manage to find a stable game under those conditions, more power to you. It's gonna be a great game since everyone shares your priorities with the same intensity.) Or accept the imperfect game you have. And at some point, the imperfect game you have might not be worth the effort. Not everything good lasts...
[X] Attending a concert, going to a play-off viewing party, going on a date, playing another game (with a different group, genre, game type, etc), etc.
 Seriously, there is nothing annoys me more than a person who tries to use empty threats as motivators. I was once part of a volunteer organization where one personal with a leadership role who emptily threaten physical violence if you missed a deadline. She was a small woman who would say stuff like, "Turn in X on time! Don't make me find you! I will hurt you!" When everyone knew she couldn't and wouldn't do that. It doesn't make her sound serious, or imposing. It just emphasized her relative impotence.