If that voice assistant were self hosted in the little device, I agree. But those simple interfaces are connected directly to a significantly larger machine that literally knows everything about you and half of everyone you know. It's not unheard of to expect it to be more useful than setting timers and playing music.
They "know" a bunch of discrete facts. They don't know that if you book me on a red-eye unnecessarily to save $100 I'll be hunting you down. Or any of a zillion other flexible preferences--some of which I'm not even very consistent about.
I don't know about you personally, but google definitely knows I've never booked a red-eye and that I haven't booked a layover since the early aughts. I'm fairly sure Google could easily figure out not only where I'd be interested in flying to in the next few months, but when and for how long, and at what price points I'd consider upgrading my flight.
I know they know this about me not only because of my Gmail account but also because I use Google flights to find the flights before I book them.
Unfortunately they're not using this data to help me. Rather they're using it to target advertising to me. But they definitely have the data and the machinery to be more useful to me with more than just a few facts
Maybe my travel is more complicated but I even not infrequently get annoyed with "past me" for various travel-related decisions. I avoid red-eyes but at some price point I won't--or maybe only if it's someone else's money. And maybe I don't have a choice based on my schedule or just what flights are available. Normally I won't do an unnecessary layover but maybe I will to fly my preferred airline.
It gets complicated in a hurry and for the cases where it is relatively simple (and when it gets into very complex international travel a voice interface is going to be completely useless), I can look up my options pretty quickly on a computer.
