Here's some cool insight into how language works. (I knew someone was going to point out Coach Baker's programme, maybe or maybe not as a gotcha.)
Language is never made up by singular persons, but is instead made up by (and so of) non-singular people. A language can be described as "dead" if no (native) speakers converse in it anymore. Latin is a cool example, not only cos it's a cool language, but also because the point is really clear. Despite all the studying of Latin that still takes place, Latin is considered "dead" in the sense that no one holds conversations or writes texts in Latin anymore. Now, you can object and name me a few outliers, but that proves my earlier point: non-singular people. You need a decently sized demographic speaking a language naturally, organically, for a language to be "alive".
Because "alive" denotes a state of language as being open, most notably to new lexical items, i.e. "words". Vocabulary words are the unstable elements in language: they change over time, become obsolete, and are invented practically every day. Words are necessary -nomen for new phenom-s. When a new technology hits, new words always follow. Take for instance the invention & popularisation of the computer and internet. All of a sudden you get software, hardware, (computer) mouse, (computer) monitor, broadband, bandwidth, and IT-specialist. These things happen very naturally. You have new objects and roles, and now you need new words for it. Most of the time, these types of new words are very straightforward, very similar to how most towns and cities are toponyms, literally place names. Words in this sense become a referential tool to refer to something concrete in the real world.
The interesting part in all this is that words can be used to refer to things not in the real world. Something like a dream or complex thought is harder to put into words precisely because a simple reference won't do. Following this line of thinking, one could argue that every lengthy book is nothing more than a multi-word attempt at referring to something specific in the author's mind. But that would be tangential to this forum post. What isn't tangential, however, is people referring to new things with new words. In this case, the practice of combining strength training with bodybuilding. Now, any seasoned lifter would agree that strength training benefits from necessary assistance, and that this assistance can come in the form of exercises traditionally at home in a bodybuilding environment. But human beings, being linguistic beings, like being lazy. So that gets, first of all neglected in the pretense that strength training is somehow exclusively squats always, and second shortened to a new word. (The newness of the word can and should be discussed, too, since the first attempt at something is hardly ever the one that survives, that gets popular. But I don't think I have room for that here.)
To the very much unneeded defence of Coach Baker, the use of the word "powerbuilding" does not in itself constitute either an approval or condemnation on the part of the (language) user. In exactly so many words, what Baker did was to pick in on the fact that this word is out there, it "exists", people use it, and market appropriately. For Baker to tap into a market of fencesitters who'd like to be strong, but would also like to do curls, he can do much worse than use the word "powerbuilding". Instead, he could try to make a bloviatingly long post like mine in an attempt to dissuade people from saying that word. In truth, no one is near powerful enough to make (non-singular, don't forget) people stop saying words through direct appeals and rhetoric. And so the easy, and only solution, is to just join in.
Not that I can speak for Coach Baker, of course, but I thought I'd give you a reasoned seasoned explanation for a linguistic phenomenon as it is happening with a very relateable topic. Cool, eh?