1. It is the fastest way to build. Auth, notifications, DB, cloud functions, analytics. You have everything you need.
2. Generous pricing. You will be able to get most of the things done with minimal costs on infra.
3. Dev Friendly: Anybody who comes with firebase alternatives, I always look at the toolset. If you look at Firebase, the CLI is amazing.
On top of this, I simply love their emulators. You can test everything before hitting production. All in all, I simply love firebase. If they are able to get the cloud functions with go runtime it will be so nice. (Right now the option is to use Google cloud functions).
But what I really mean is that it would be cool to have Firebase db access SDKs and realtime capabilities, with a relational, non-proprietary database. If you plug in your CloudSQL or another managed database you don't get that, and have to write everything on your own.
Supabase seems to be going in this direction, and while I haven't tried them yet, I certainly see how it's an attractive proposition.
That said, if I attend today and ignore sponsorships, I'd actually get DigitalOcean market place deployment of Appwrite. I honestly think it's quicker to get started with, and I like owning my data ;)