Because human progress is not an event. The main task of news networks and newspapers are to report on things that just happened, so to get to proper analyses and status updates, you have to dig deeper.

There are reports on new scientific discoveries all the time. Unfortunately, a lot of them are taken out of context or dumbed down for the lowest common denominator. A lot of exciting scientific discoveries would seem like really tiny, unimportant steps, or just plain incomprehensible, to people who aren't familiar with the field. I guess the exception is new technologies soon to be made available to consumers.

Besides, there's Negativity Bias to consider. Even if there are good news, our minds automatically weigh them less than bad news. And if the news are about someone doing something good like rescuing people, it's usually a result of a disaster.

I've heard people say before that the "24 hour news cycle is incentivized for conflict" and that the quality of news in general is down because they're out to make money, but I'm sure someone else could explain this better.