One possible explanation is that the FM7(13) is really the same chord as the Dm9; only the bass changes.
The FM7(13) will likely include something like
E A C D up top (or something like it), which are the exact pitches you'll have in the Dm9. You may want to add in an F in the upper voice of the Dm9, but of course you had that F in the bass of the FM7(13).
Especially since you're playing this after what seems like a full measure of FM7(13), the Dm9 just isn't enough to actually sound like a change in harmony, and so the harmonic rhythm suddenly stagnates.
(Note: You could make a very good case that the C9 and Gmadd6 are the same chords with just a change in bass, but a) this could just be jumping to an inversion of the dominant C9, and b) this makes it a one-measure harmonic rhythm, not an FM7(13) that lasts for more than a full measure.)
One way that may add in some interest and allow you to move into a Dm9 would be to give it a little tonicizing chord. Something as simple as an A7/E that connects from the FM7(13) into the Dm9 makes the progression sound much better to my ears.