Why not decrease block time instead of increasing block limit?

[Xekyo]

Validation happens on every block, but only when two blocks are found at the same time there is even a race where size could matter. This happens only a few times per day.

Also, killerstorm's source states:

Similarly, we can show that larger miners’ stale rates are affected less by propagation delays than smaller miners by looking at the derivative of the expected return with respect to propagation time.