I worked on the Dart team at around that time. After integrating Dart into Chrome was cancelled, the team got moved from Chrome to Ads, because Ads was migratin

I worked on the Dart team at around that time. After integrating Dart into Chrome was cancelled, the team got moved from Chrome to Ads, because Ads was migrating all their websites from GWT to Dart. This isn't something anyone outside Google cares about, but it meant that it was consistently staffed as they looked for other big customers. Also, the ads codebase is enormous, so there are plenty of technical challenges from getting language infrastructure to scale to their needs. (Consider getting a language server for an IDE to scale up as a codebase grows, or making the language tools generate efficient JavaScript that's not unreasonably slow to download, or loading and displaying large tables in the browser.) I have no idea whether Flutter generates revenue directly. I'd guess not, but internal usage of Flutter is likely enough to justify having a team devoted to maintaining and improving it.