Effects of increased income over short and long run in AD-AS equilibrium model
Because higher wages do not necessarily mean that national income increased. From macroeconomic perspective national income is output. Higher wages in these simple models do not necessarily translate into higher output. 

For example if these higher wages come from company’s profit then on one hand one (worker) household income increases but another (entrepreneur) household income decreases. Assuming all households have the same marginal propensity to consume this would not affect aggregate demand or national income. This is not necessarily realistic assumptions and there are more complex models that relax it, in that case higher wages could boost aggregate demand.

Also the side note is the same question you already asked here.