After tones of feedbacks, Amlogic finds out that most of their TV box users do not need the specification 4K@60fps at all.
Amlogic wants a cost effective SoC in the market to fight against RK3229, for this very reason, they decided to have 4K@60fps resolution spec removed. Hence limiting frames per second rate to 4K@30fps instead.
To be simple:
S905X: 4K@30fps + 4K@60fps