It started as part of the modern.ie project, which would distribute Windows VMs to the primarily Mac using web developers at the time so they could test against

It started as part of the modern.ie project, which would distribute Windows VMs to the primarily Mac using web developers at the time so they could test against Internet Explorer, countering the trend of just telling people to switch to Chrome if they complained about broken functionality. The VMs were time locked I believe and would shut down after a few hours (at least the more recent ones do).