Spaces is just a directory of text rooms. Users don't just join every single room and rooms are independent from each other instead of having a single roles system shared between the whole server. In this model having an announcements channel wouldn't work since there will be people who didn't join the channel. Similarly people might not want to join a rules channel.

A simple directory of rooms that you can join is still very far away from the way Discord works. Matrix is still focused around users joining rooms which where Discord is focused around users joining servers.

At least in the mobile app I didn't even know this existed. To find this directory of rooms you need to open up the spaces drawer. The you need to open a menu for the space by clicking on a stack of three vertical dots. I thought this would have things like settings or something in it, but no this is the way to navigate to important information. Then you need to click on explore rooms. You now can see a list of rooms you can join. You can now join a room with a tap. Then you have to open the room with a tap. This is extremely convoluted and hidden.

Meanwhile Discord doesn't need this whole process since you don't need to manually join rooms yourself.