I think they are able. Apple still arguably does. But there's no obvious incentive for them. Developing your own browser engine is a big ongoing investment, constantly adding new features and promptly plugging security vulnerabilities. We've long expected browsers to be free, so it doesn't generate any direct income. If they want to collect data with it, they can wrap Blink in their own app.
Mozilla keeps it up because of the principle that there should be more than one decent rendering engine. For-profit companies can't take that stance.
