From what I've seen most languages don't want to have a Turing complete type system, but end up with one anyway. It doesn't take much, so it's easy to end up with it accidentally and/or by adding conveniences that don't seem programmable, e.g. associated types and type equality.
Fun rabbit hole, in since cases they think it's the result of cells from offspring winding up in the wrong side of the umbilical but there are also cases where there was never a pregnancy in which case it has to be wayward sperm but that's absolutely bizarre and far too orthogonal to the sperms primary objective.
And AFAIK they don't have any idea of why this is beneficial to the woman or even to the man who created the invasive cells.
[1] https://en.wikipedia.org/wiki/Heterosis