because the version has reached its official end-of-life status. Autodesk typically only provides trial downloads for the current version and sometimes up to three years back Autodesk Community, Autodesk Forums, Autodesk Forum Official Availability and Access
Always download directly from Autodesk’s official website or authorized partners. Autocad 2017 Trial Version Free Download
This takes 15–30 minutes depending on your hard drive speed. because the version has reached its official end-of-life