There are, in essence, two "layers" of federal law. The Constitution, and the body of laws passed by Congress.
The Constitution cannot be changed by Congress directly, and in any case, the process of doing so is, by design, slow and complicated.
A law, by contrast, can be altered, overturned, or replaced in technically as little as a day, if the leadership and majority of both houses of Congress and the Presidency are all on board and co-ordinate, although a few weeks is much more normal.
To give an example of what I mean, consider the (somewhat) recent executive decree made by President Trump to block entry from citizens of six countries to the United States. At the moment, it is being challenged in the court system at time of writing. There are several challenges pending at the moment: some of them based on Constitutional claims, others based on legal claims. For example, two particular challenges are based on violations of the Establishment Clause of the Constitution and of the Immigration and Nationality Act of 1965 (a law).
Let us, for the sake of argument, say that a majority of each of the houses of the US Congress supported the executive order. If the executive order was blocked on the basis of violating the Immigration and Nationality Act of 1965, Congress could repeal or amend the act to allow the executive order. (Congress made the act in the first place, and any thing Congress does, Congress can undo).
If the executive order was blocked on the basis of violating the Establishment Clause, Congress cannot re-write the Constitution (single-handedly; they can start the process but it also involves confirmation by a three-forths majority of states (either through legislatures or conventions).
EDIT: Upon re-reading your question and your comment, I would like to make this more clear. While the Supreme Court can only overturn a law on constitutional grounds (i.e. it violates a rule set forth in the Constitution), they can block applications and enforcement of the law on legal grounds (i.e. it violates a rule set forth in a law passed by Congress). The Supreme Court deals with more than "mere" Constitutional issues, as they are the ultimate court of appeal* for all federal cases in the US.
*Any federal case (and many state cases) can be appealed to the Supreme Court, however, the Supreme Court has the ability to decide which cases it wishes to hear.