What I'm about to say only applies with a constitution like ours that's written as a legal document.
I think everyone can agree the job of the courts is to apply the general law to specific situations. Before they can do that, they have to determine what law applies, and sometimes multiple apparently applicable laws will be in conflict with each other. Example: municipal ordinance saying black people aren't allowed in public parks vs. state law saying municipalities can't discriminate against people based on race. To deal with that you have the principle that higher laws trump lower laws, so you apply the higher law. In my example, if the city tries to prosecute a black person for entering a public park the judge should throw out the case because the city doesn't have the legal authority to do that.
The constitution is the founding legal document of this country, from which all legal authority flows. So if a government entity attempts an act forbidden by the constitution it stands to reason that in cases brought before them the courts should apply the higher law, the constitution, and refuse to enforce the forbidden action as being invalid. Just like they would if a city attempted an act forbidden by state law.
To take an obviously extreme example, what if congress made a law saying that if someone refused to answer police questions on the basis that the answers would be self-incriminating (Fifth Amendment) they could be charged with obstruction of justice? Should the courts allow those prosecutions to go forward? I think everyone would agree that they should not.
It should also be noted that the federal courts at least will not take hypothetical questions. It's not enough to say "this law is unconstitutional", there must be a specific person alleging that their rights specifically have been violated. And more often than not the court will simply say "it's unconstitutional to apply the law in this instance", rather than that the law as a whole is unconstitutional.
Without judicial review there's nothing stopping the federal government from just completely seizing all legislative authority over all subjects.