The release notes on that page clearly state why the package is not present there:
Windows packages for EnergyPlus 8.6.0
and prior had a vulnerability in the
View3D binary that could expose users
to a stack-based buffer overflow.
Because of this, all Windows packages
8.6.0 and older have been purged and are no longer available. We apologize
for any inconvenience.
The EnergyPlus program itself is not vulnerable, only the View3D binary. However, to protect the people using our tools, we are no longer able to distribute old installers that include this binary. You are welcome to build EnergyPlus 8.6.0 from source if you would like, though I would highly suggest updating to a more recent version, as that version is now three years old.