The reason we have custom roms on android phones, is because of Linux's copyleft license: Phone vendors are required to publish their kernel modifications shipped with their devices.
This already reduces e-waste by lowering the purchases of new phones, when old ones are perfectly functional.
Thus, copyleft helped the environment
To me this is also an example of how the GPL fails. The requirement for phone vendors to publish their Linux source trees does in part enable custom ROMs, but vendors still have found ways around the license in the form of proprietary kernel modules. This gives these phones a shelf life: after the latest OS version requires a kernel newer than the one the proprietary modules are shipped with, and efforts to write shims (which are always error-prone and hacky) start to fail, the phone can't even get updated versions of the custom ROM.
