For me: I need services that support the UI, as well as a public-facing API with basically the same data. I don't have the time/resources to build/maintain them separately, and my perception is that GraphQL and the wider ecosystem around it haven't yet reached the same level of ubiquity/maturity as plain-old REST.
A single, well-designed REST API that can be consumed by my own UI as well as public clients is how I'd prefer to handle it right now.