The history of the VMs is that many years before there was QML there was QtScript. A Javascript based engine. This got used for Qt4. In Qt5 the V8 open source

The history of the VMs is that many years before there was QML there was QtScript. A Javascript based engine. This got used for Qt4. In Qt5 the V8 open source engine got used instead. Either way, they ended up picking something that was already there, which would explain why it was easier than creating a brand new langauge.