I would imagine they don't know what demand for this will be like, and parts for older devices are probably not in production at this point - so they probably don't have inventory to support a lot more than what they expected to service through their traditional processes.
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While not self-service, I'll note they've expanded service lifespans on the Mac side for repair in recent years. They'd previously guaranteed service would be available for 5 years (from end of new production of the model - which could be a while later than you purchased yours. The mid-2012 13" MBP is still less than 5 years from end of production.), but it was a hard cutoff after that. 5 years and 1 month? Nothing.
Now it's up to 7 years if the parts are available (10 years for batteries on some models), and anecdotally we've had a few repaired in that age range without issue.
That direction suggests to me that in the long run you're likely to see similar things on their "self-service repair" side.