Because fuzzers build with "use_libfuzzer=true is_debug=true" doesn't support debugging well (gdb cannot print local variables)
(btw, is it a bug? I assume it is known limitation.)

I often build fuzzers with "use_libfuzzer=false is_debug=true". However, it assumes all command line arguments arg files, not directories.
Sometimes I can workaround by shell wildcard, but not always (argument too long because too many files in corpus directory).

Supporting directory is helpful for bugs due to persistent state of fuzzers.