Why no sanctions against Egypt's brutal regime?

Because the last thing Egypt needs at the moment is it's economy damaged. High unemployment and Inflation which result from sanctions combined with the current tensions out there have the potential to send the country down the path of civil war.

Sanctions rarely work, and are only effective against an embedded government.

the US never say this about Iran

Iran has a stable regime. Sanctions are imposed on Iran by the UN to stop that regimes actions.

Iran = Stable Regime
Egypt = Unstable regime.

Iran wasn't stable when there were riots