If they didn't destroy Bitcoin is not because they never wanted to, but because they can't.
They can't?
1: Spend the necessary capital to 51% attack the network. Destroy it.
Good luck creating another bitcoin that people will trust after that.
2: Wire $20M-$50M on various bitcoin exchanges and short it down to single digits and beyond in one go totally destroying confidence.
Currently there are around $15M in bids (lol) on all major exchanges combined and plenty of longs that can be completely margin called ($23M+ on bitfinex alone for example), it should be fairly easy.
Not only $20M-$50M is nothing for them if they are inclined in "killing" BTC, they would also make a very good profit on top of it.
They
could destroy bitcoin is they wanted to. Thing is, they probably DGAF.
That won't destroy bitcoin, it will just make its user base smaller in the short term.
From there it will grow again. It has to, it's too useful to just "go away".
Bitcoin (the neutral money concept) can't be destroyed as long as there's a group of people who desire it. I don't think people will stop desiring it, ever.
Attacks from the state (propaganda, threats, DOS) may prevent bitcoin from going fully mainstream, but even if it remains niche, it will likely be a larger niche than it occupies today.