I wouldn't generalize the whole US goverment because there are different people with different opinions but there are powerful groups and lobby that want to control everything including bitcoin. They have a right to do this because they think that even if $1 is involved they can interfere. That's why many crypto-exchanges don't allow US citizens to use their services or platfroms.
Since $ is widely used in commerce and as a reserved currency that's why they have real power over many other jurisdictions or...they may impose different sanctions on those who disobey.
World financial system simply can not operate without US that's why many have to listen to SEC and FinCEN say about bitcoin and other cryptocurrencies otherwise they won't be able to operate or be very limited. Look at Iran for example.