Why don't portmanteau words catch on?
Going over many sources of slang, one thing that pops out is how abysmal the success rate is for portmanteau words. That's where you cut out pieces from two words and splice them together, the new word suggesting some combination of the two original words. Like "Rethuglican" from "thug" and "Republican" -- won't last.
Here we see the main problem with these words: they're too self-aware, and every use is an overly eager attempt to make the listener laugh. "Huh-huh, Rethuglicans -- get it?" Yeah, we get it, you moron. Oral communication is not very conscious, since that's the mode we're adapted to, and so anything that halts the flow of speech in a conversation won't take off the ground. That's why you find those obsessed with portmanteau words in the nerdy parts of the literate culture.
The few good portmanteau words are totally transparent as for the two words joined in surgery, and also what is implied. "Stagflation" works because only one word will come to anyone's mind that beings with "stag-", and only one that ends in "-flation". If you were paying attention to the economy in the '70s, it wasn't too hard to see what was meant. And unlike "Rethuglican," the term isn't meant to be a self-aware joke every time it's uttered. It's not a put-down of the out-group by the in-group, but a term that united everyone who felt like the economy was the worst of both worlds back then.
Even a seemingly straightforward combo like "netiquette" requires a moment's pause to get what they mean. Obviously one of the words is "etiquette," but lots of words begin with "n-". Oh wait, it's the entire word "net" that's been spliced in. OK, so you mean like etiquette on the internet? Damn, though, why did you have to make me think so hard about it -- just say "online etiquette" or "internet manners" or something simple.
Pleasing ornamentation makes the thing easier to recall (for example through repetition), and most portmanteau words do the opposite, making us reflect consciously on the derivation, rather than retrieve it automatically, and even more quickly than we would if it lacked a nice little ornament. "Back-breaking" work, a "ball-busting" wife, or some fat "cockblock" with a "tramp stamp" -- those are reliable repetition-for-memory devices at work, giving these neologisms an infectious quality.
This highlights a key weakness of portmanteau words -- they are designed for self-aggrandizement (look at how clever I am), whereas alliterative and rhyming phrases are designed for the benefit of the listener (easier to recall). Oral culture tends to be pretty egalitarian, so new words that violate that ethos are doomed from the start. They'll only be successful, if at all, in a literary context, and even then only when there's a personality cult -- why else would you help to regularly boost someone else's status?
(That distinguishes them from another autistic favorite, the acronym, which as nerdy as it is, still does not pretend to be a clever turn of phrase. Its total lack of imagination maintains the egalitarian ethos of the group that uses it.)
So, the more self-regarding and the more cut-off from other people you are in real life, the more likely you are to rely on portmanteau words. That has to be why they litter just about all science-fiction writing. The enjoyable and empathetic ones like Philip K. Dick try to keep them to a minimum, although even he can't help himself sometimes, like "mentufacturer." A transparent compound like "empathy box" works so much better.
Skimming through a list of words and phrases coined by Shakespeare, I didn't find any portmanteau examples. There's plenty of alliteration, though -- bated breath, dead as a doornail, fancy-free, kill with kindness, lackluster, primrose path, short shrift, and so on.
It would be hard to study pormanteau coining over time, since they are so unsuccessful. Still, it seems like over the past 20 years we've gotten more carried away with them -- netiquette, e-tail, Rethuglican, glibertarian, etc. One clear consequence of our declining oral culture is our growing inability to coin infectious new words, which relies so much on the sounds of speech. We think that just because a bunch of dorks use some buzzword on Twitter, it's got legs. Unless it's technical jargon, though, a word like that with little use in speech has little chance of survival.