tl; dr: I think the team can prioritize its time and efforts better, especially around new development.
At this point you’ve all probably seen https://core.trac.wordpress.org/ticket/26527
If this had been raised a week ago, would have been no problem. Plenty of time to create and test a fix.
The meta-issue is that this is an easy catch, and keyboard accessibility is on every basic accessibility checklist. It’s been present since the very earliest days of the THX plugin.
As we do features as plugins, it’s really important that this group run and test those plugins every week to provide the perspective, experience, and patches to ensure the plugins meet the high standards of accessibility we set for ourselves. Even if a feature plugin never comes into core, it might become the canonical implementation of a given idea and be popular on its own right, and so worth investing time into.