Essentially "system integration" of radio modules- naive to expect "turn-key anything at 5 GHz ;-) FEM, LNA, switchs, filters & diplexers used to leverage reference design of chipset vendors. Modules lag chipsets by 1-2 years. Certain chipset vendors, i.,e Atheros, put the 5 GHz outside ther chipset/module, so somewhat forced to "roll your own." Difficult to get support form chipset vendors (understandably) if volumes are below ca. 1M/month. Antenna integration/matching, and conducted vs, radiated (OTA) RF performance are constant issues. Also, regulatory compliance is expensive & time-consuming, esp. if lots of countries involved, & 5 GHz much more "scattered" than 2.4 GHz.