The issue, based on my read, is that lots of existing applications, many of whom are proprietary and may not be supported by their vendors, _depend_ on ABI stab

The issue, based on my read, is that lots of existing applications, many of whom are proprietary and may not be supported by their vendors, _depend_ on ABI stability, and a break cause these applications to simply fail, for what appears like no good reason (how many businesses care that their legacy app broke because of supporting a niche CPU architecture?). That's the big issue here, and the historical reason for caution.