They could... But that ship has sailed IMO. Like with the silk road case, some FBI agents apparently took some BTC for themselves. Politicians, businesses and countries are themselves holders of bitcoin and the incentive is to play along. Democratic politicians like to get the popular vote and bitcoin has now become a mainstream popular thing now (whether we like that or not).
Bitcoin is too big. A trillion dollar market cap says something. Of course they won't just let their power go so easily which is why I think their best strategy of attack is just to tax harder.
As for monero, I think its just too small and unfortunately has a bad branding problem too. Not that I personally care about that. It has better privacy that bitcoin, but nothing else (network effects, fair distribution, decentralization, story etc).
Also privacy will improve on bitcoin as it goes on. There are countless projects working to improve different aapects of bitcoin that no one can keep up with it all.
You should look for some of these projects. I bet there are some trying to use monero properties on a pool of bitcoin. If there isn't, then you should start one.