Aren't they doing this because not enough electricity being used at night is bad for them anyway ?

Depends on the generators in the system. Certain types of generators don't like / can't really / doesn't make sense to spin down much (e.g. nuclear, hydro). A nuclear reaction is going to generate as much heat as it does, you don't dial down a knob. A dam has (usually) a given amount of water flowing through based on external circumstances, not electric demand. Compare that with a coal generator, where you can just stop shoveling in more coal to reduce heat output.

Sorta like that.

I wouldn't really classify it as "bad for them", more like it's gonna be wasted anyways.

Note: been a decade since I studied power systems, so... inaccuracies abound.

That's been around for decades. Electricity at peak hours is more expensive than at any other time, so anything to move demand from peak hours to off-peak hours is good. Laundry is especially bad because electric dryers are very energy intensive and people tend to run them in early evening hours after getting home from work, when electrical demand is at its peak.