I believe that this question has to do with about the Supreme Court’s ruling in the case of Katz v. United States. Therefore, I have edited your question and moved it.
If you are indeed asking about the Katz case, the reason that the Court rejected the trespass doctrine was because they thought that it was too narrow and limited. The Court wanted to expand the way the 4th Amendment was interpreted.
The Supreme Court had defined the trespass doctrine in the case of Olmstead v. United States. They had said that the 4th Amendment only applied in cases where there was an actual physical trespass into a given place. An amplifying device on the outside of a phone booth (such as was used to listen to Katz’s phone calls) would not have constituted a physical trespass. What this meant is that it was physical spaces that were protected from warrantless searches.
In Katz, the Court said that it was people, and not physical spaces, that were protected by the 4th Amendment. They said that the question of physical trespass was not relevant. Instead, they argued that Katz had expected to have privacy and therefore he was protected from a warrantless search. It was he, and not the physical area of the phone booth, that was protected from the search.
Thus, the trespass doctrine was rejected because this was the Warren Court and the Warren Court was interested in expanding people’s rights under the 4th Amendment.