Should Ford also be required to make parts for the Model A? At some point a company has to stop supporting old outdated products.
There are parts suppliers other than the OEM. Part of the problem with software is the length of copyright, and the fact that some may claim distributing a patch would be copyright infringement.
Instead of mandating a fixed time frame that support must be provided, would it make any sense to tie continued copyright protection with continued support? That would allow the manufacturer to determine how long they wish to provide support, and also allow interested third parties fill the void later.