I would think it is because of how "modules" can effectively be "bolted" on top of existing things quite easily.
Consider putting a new "module" on a bicycle. If you were doing it statically, it would have to have the screws in the proper place to be able to attach as it needs. Dynamically, however, you just use a zip tie to hold your piece onto the bike.
To be sure, if you buy a nice bike, many of the common attachments have "static" points where things can be added. If you want to place a holder for a phone, however, you are much more likely to do something that is much more adaptable at fitting things on.
> Dynamic languages are naturally more modular
Why is that? I'm pretty convinced pure and especially lazy languages allow for great modularity.
See http://augustss.blogspot.nl/2011/05/more-points-for-lazy-eva... for an interesting view on this.