The only certification requirement for crosswind is the 20% Vs0 requirement in para 237, and it never exceeds 25 knots. So none of those numbers were driven by a (Part 25) requirement.
I'd bet that each of them is simply the best they could demonstrate on the day(s) allocated to chasing winds during the certification programme. The version of the A320 limitations I can easily check indicates that those are "demonstrated" limits, not necessarily limiting for the aircraft (although operators may apply them as limits by choice, of course).
And I can't conceive of any linkage to VMC. Appart from anything else, the idea of doing a VMCG test with a (adverse) 29 knot crosswind makes my toes curl!