Date picker uses calendar widgets
Even thought the date picker is a "nice to have" for the date entry field which is accessible, deque's interpretation of WCAG says it is not sufficient.
A calendar picker is not accessible via keyboard. Only mouse users can access (see) the calendar and pick dates directly from the calendar. Keyboard only users must use an edit field to enter the date, and they cannot see the calendar. This fails because the keyboard only user is at a disadvantage because they cannot see all the information that the calendar view provides.