Why constructors of a class with a virtual base class cannot be constexpr?

The restriction hasn't been changed since C++11, and the corresponding restriction for destructors were added in C++20. The newly adopted P2448R2 talked about this, but didn't touch the reason.

Perhaps it was N1980 (the proposal for constexpr before ) that added this restriction at first, but I failed to find the reason or motivation in it.

I also wonder whether there's anyone wanting to relax this restriction.