Why couldn't bastards inherit titles?

Question

Why were bastards historically not able to inherit nobility or monarchy from their parents? What about being a bastard made one unfit to rule? For example William IV of the UK was succeeded by his niece Queen Victoria instead of any of his children because all 10 of them were bastards.

Answer 1

Laws of inheritance excluded bastards because such products of illicit unions undermined the institution of marriage. Among people of titles and property, marriage originated as a legal contract between families that validated social position and fortified financial security. Whether the man and woman loved each other was beside the point. Legitimacy was crucial to preserving authentic blood ties. One could argue, too, that in a patriarchal society, excluding illegitimate children allowed men to pursue sexual relationships with little consequence beyond the moral imperative of providing financial support for such children. For royalty, these inheritance stakes were higher because marriages were contracted for diplomatic and even military reasons and to preserve the highly exclusive world that preserved the social power of dynasties.