Not sure if someone's already asked this before, but really, why is that?
Every other division seems to have fairly balanced proportions of wrestlers, strikers, submission specialists, and brawlers, but these two divisions are outliers for how packed they are with wrestlers. Here's a quick, rough count of wrestlers in the top 25 rankings for each division:
HW: Cormier, D. Henderson, Velasquez, Barnett - 4
LHW: Jones, Davis, D. Henderson, Evans, Bader, Lawal, Ortiz, Matyushenko, Couture - 9
MW: Sonnen, Munoz, Weidman, Okami - 4
WW: St-Pierre, Ellenberger, Koscheck, Hendricks, Fitch, Shields, Sanchez, Story, Woodley, Brenneman, Askren, Hieron, A. Johnson, Pierce - 14
LW: B. Henderson, Edgar, Maynard, Melendez, Miller, Guida, Chandler, Guillard, Thomson, Volkmann, Healy, Alvarez - 12
FW: Mendes, Curran, Kawajiri, Griffin, Elkins, Warren - 6
BW: Cruz, Faber, Jorgensen, Benavidez, D. Johnson - 5
LHW is realistically shorter because Couture's retired and Ortiz will probably retire after his rematch with Griffin. BW is also realistically shorter because Benavidez and Mighty Mouse moved down to flyweight. Lastly, Dan Henderson doesn't fight at HW at the moment, so HW should be more like 3 wrestlers.
But yeah, 14 in WW, and 12 in LW. That's not even including the fact that the wrestlers aren't just top 25 fighters, but they're heavily focused in the top 5 and top 10 rankings. Of the top 10 LW's who aren't wrestlers, you have only 3 - Pettis, Aoki, and Diaz. WW has 4 non-wrestlers in the top 10 - Penn, Diaz, Condit, and Kampmann.