Sorry, support costs. (Rhetorical) Why would you think it would be free ?
The Make editions are unsupported.
You should really have read the terms of Service.
8. Support and Maintenance
Trimble provides the support and maintenance services for SketchUp Pro for an additional fee pursuant to its standard service terms which are available upon request from Trimble or at http://help.sketchup.com/en/policy. Support and maintenance services are not available for SketchUp Make.
(Emphasis by me.)
That said, from time to time they are interested in how model files get corrupted, so that they can fix bugs.
But your models are from version 8, a nearly 5 year old version (v8M3,) that has been unsupported (all editions) for more than 2 years (as of last November 3rd.)