ABAP programmers don’t explore the possibilities of SQL, probably for historical reasons. There are many who instead of using INNER JOINs still think it’s faster to do several SELECTs for internal tables and then process the data in ABAP. But the truth is that even if there are exceptions, the rule is: the lower the number of accesses to the database, the better the performance. And it makes sense because, after all, they were written explicitly for this; relational databases are much more adept at processing relational data than an ABAP program.
There are of course things that, due to their complexity, cannot be done with a simple INNER JOIN. Nevertheless, some of these things can be done in a single SELECT.