Electricity travels at the speed of light, so there's a huge dependency on spinning generator inertia to keep a stable supply. With renewables, this "grid inertia" is greatly reduced.
The reduction in grid inertia makes quick demand reduction important. It takes most generation sources several seconds to "spin up" and support load transients. Loads on the other hand can be cut within a few hundred milliseconds. HVAC is nearly ideal for load cuts because they use a ton of power and small variations in temperature can be absorbed by thermal inertia of buildings and product being cooled.
There's a great document on this and how it affects the Texas grid. https://www.nrel.gov/docs/fy20osti/73856.pdf
People that willingly sign up for these programs then complain about it is a classic "leapords ate my face" scenario. The same thing happened to users of Griddy during the huge grid failure earlier this year. Griddy exposed users to realtime spot energy pricing which pegs at $9000/mwh when there's more demand than available generation.
A side note, ironically the same document praising ERCOT's innovative handling of renewable sources says the US national east/west grids are unlikely to face the same problems until the 2040's. Basically, if Texas grid was connected to one of the national ones, these problems they're trying to solve with innovation would just go away for at least 20 years.