Instead of this Game & Watch why not make a Game Boy Classic?
I imagine Nintendo only released the NES Classic Edition and SNES Classic Edition because it needed the revenue what with Wii U........... being Wii U. Nintendo can always go back to the well to make its fiscal year look a little better. With Switch cleaning up, we didn't get a Nintendo 64 Classic Edition which seemed like an obvious release in 2018 with or without Rare. To answer your question: Because Nintendo doesn't need to. If the Switch successor is just "Wii U: Part II - The Reckoning", maybe we'll see a Game Boy Classic Edition (and Nintendo 64 Classic Edition for that matter).
This Super Mario Bros. Game & Watch is also $49.99 for two 35 year old games. As stupid as this thing is, it's going to sell out. I mean, I want one, and I have no need for it. Nintendo could sell that forever and never lower the price.