99% of freely available "mp3/wav/audio-format-x to midi" converters are mono audio to midi type 0 converters. Commercial solutions may exist, though.
What your converter is doing is searching for transients and outputting a MIDI noteon with the note number determined by comparing the transient's frequency against a table. A full song includes thousands of these attacks, and some are overlapping one another. As such, you get garbage although the fundamental tunes and tempos of the song can be salvaged.