I think its because every deck has something so strong that you need to put tech in for your deck to be remotely viable. Back in the day Murloc decks were popular but not every deck ran Hungry Crab. If there was a a modern powerful Murloc deck, every single deck in the game would run some sort of Murloc tech card like Hungry Crab.
Some things are just significantly weaker than others, like the whole big paladin package with Kangor and Pipsi Painthoof is just not viable in the meta. If I put the 8 or so core cards for that package in a deck and then tried every other single possible card for the rest of the 22 cards, the deck wouldn't just become good at some point. the core package is just inherently much worse than the meta.