[Shank]

There are a lot of factors in-play that make realtime grid balancing harder. You can have more capacity on paper but have things trip offline due to faults, overloads, unexpected maintenance, etc. Just because you have the capacity on paper doesn't mean that you can always start that capacity up, route the power on enough transmission lines, etc. There are multiple wildfires and it's a very hot day right now, which can create adverse conditions.

I definitely suggest Practical Engineering's power grid series for a better explanation about how this stuff works, but grid balancing is certainly nontrivial.

Edit: You can actually see realtime transmission outage data via OASIS (http://oasis.caiso.com/mrioasis/logon.do), under the Transmission -> Transmission Outages tab. There are other tabs in OASIS that show related grid factors too.