The main function of the journal is to assess the quality of the paper and to accept or reject based on that assessment. The decision may or may not be supported by a report, which I understand is optional.
In the current system, with very little if any reward for refereeing, the referee may not feel motivated enough to invest more time into writing an extensive report, unfortunately.
In particular, the rejection decision may be based on a "quick opinion" of an expert, in which case no report is needed.
However, in case of rejection, some reason should be named.
In other cases, the journal has hard time finding a referee.
Or the referee became unresponsive and the editor has to ask someone else,
that can repeat a few times, until the editor gives up and returns the paper,
again, without any report.
Especially if the paper is difficult to read and understand
but the referees do not want to reject simply based on the paper's (un)readability.