Gnome isn't locked-in. For being an important open source project, AWS has given Gnome credits so that they can use AWS free of charge for years. Once those credits expire, they are free to leave. So long as they do their proper preparation to migrate away, they get multiple years of hosting for free.

Gnome has already been in this circumstance. Their free hosting from another provider expired so they moved. Though as I'm researching this, I can't find the sources I've read this from.