The belief that there is little that cannot be made subject to federal regulation is debatable. In multiple Supreme Court cases, the court has issued verdicts that favor state sovereignty. In the 2013 Supreme Court case Shelby County v. Holder, the court invalidated elements of the Voting Rights Act in part because of the Tenth Amendment. The majority opinion quotes another case, which reaffirms that the Tenth Amendment empowers states to regulate their own elections.
Even in cases that side with the federal government, there’s considerable gray area. In the 2012 case National Federation of Independent Business v. Sebelius, five court justices upheld the Affordable Care Act and the federal government’s ability to fine citizens who don’t buy healthcare. At the time, the justices averred that the law is contrary to the Commerce Clause.
For further examples, think about what’s happening during the COVID-19 pandemic. Currently, the federal government is in the hands of people who generally favor masking and vaccination. Much to the chagrin of the federal government, many states have opted not to regulate mask-wearing or vaccinations.