heavy load, burden, lift up
夯 centers on bearing a heavy weight: a physical load, a burden, or the act of lifting something heavy.
夯 combines 大 (big) and 力 (strength), suggesting great strength applied to a heavy load. The exact historical development is uncertain, but the component combination fits the meaning of lifting or bearing a burden.
Big 大 strength 力 is needed to lift a heavy load: 夯 is a burden that requires great effort.
For コウ, imagine a strong person lifting a heavy load and letting out a grunt: 'Koh!' The sound 'Koh' cues コウ while the big strength lifts the burden.