Indie gamedev company co-founder here: 14 people team, 2 games released + next in progress and signed with publisher. There are few big reasons why you can't just go and use Godot.
Publishers. Basically 3 years ago when we made our first game together using Godot it was main reason why we were rejected by some publishers. Now situation can be slightly different, but many publishers still have in-house pipeline that only work for Unity and Unreal: QA, localization and console porting.
Asset Stores. Majority of modern games are not built from scratch and selection of ready-to-use components and assets available commercially would be like 1000x for two major commercial engines.
Hiring. It's take years and several commercial projects of experience to actually become effective at using specific game engine. There are just far less Godot experts arounds especially those with experience of making commercial game while working in team.
These reasons can sound like inertia, but it took decades for Unreal and Unity to conquer their market share and build their moat. I myself big open source and Linux nerd, but sadly it's will take another decade for Godot to make sensible dent in this market.
PS: We released first game on Godot and our following projects are built on Unity.