Be honest.
If it was announced that the MCU was ending after everything ready to go was released, you don't think people would still flock to Guardians 3?
They would. Because the movie still looks amazing. Ending cinematic universe or not.
Just like people will probably see Aquaman 2 if it looks just as good. Or Flash if people want to support a criminal.
There's a huge difference here though. The quality of the films. DC has been a nightmare of terrible movies one after the other. They are 'rebooting'(ie, cancelling this current iteration of the DC Universe because it's a failure) in order to establish something more coherent and better quality. We're all aware of that.
That means they have no faith in the movies they have in their pocket which they are going to release. Will people watch them? Sure. It will be a mish mash of people who don't know/care about all this background news, people who need to be entertained, people who are curious, die hard DC fans, etc...but not that many people will go. Look at Black Adam. Arguably a box office Hollywood actor like Dwayne Johnson can't salvage that wreck...although I think he did good in the part.