I think it has at least something to do with the way steampunk shed its "punk" connotations and cyberpunk never did. Being "punk" pretty much limited it to gritty, grim settings with morally indifferent heroes.
And worse, it was cool.
This limited its repertoire, and its emotional palette. Goofy steampunk is just steampunk that is goofy, but goofiness in cyberpunk pretty much had to a parody. And has the added advantage that while straining after goofiness can make a work worse, the mere fact you can tell it's aiming at goofiness is not fatal, whereas "cool" -- well, if we can see you trying, it's not cool.
And there are a lot of other options beside goofy that cyberpunk can't pull off. A lot of fun, for instance, and many forms of moral earnestness.
Of course, that does raise the question of why only steampunk shed its punkishness.
Perhaps cyberpunk didn't really have an aesthetic separate from being punkish, and so shedding it took you out of cyberpunk entirely.