Do people actually prefer talking to bots instead of interacting with apps? Bots don't need to be installed usually, so that makes them lower barrier, but neither do websites.

They are useful when you want to query them with tasks that have a lot of degrees of freedom. These tasks may be easier to describe in human language where the user highlights the important parts forgoing the need to have a complicated GUI with lots of buttons. In these cases though, users don't know what the bot is capable off. GUIs are more discoverable because they present possible options with bad GUIs hiding even more possibilities in the submenus. This is one advantage over GUIs I would like to see bots explore.

In my experience however bots are not good at doing the right thing when queried with a task that has a lot of degrees of freedom. I own an Amazon Echo and at times I feel like I am reciting incantations to get it to do things I want from it; this is especially true of Alexa's "skills". If I have to memorize specific commands for the Echo to respond, it becomes a glorified voice operated command line to me. A verbose, inaccurate command line without a man page.