I think there was a shift with this mainly because people criticized others for using it saying that it hurt the innocent child more than it did the parents. Nowadays though the child probably would not even appreciate the original meaning of the word and would in many cases be amazed that is means a child born to unwed parents.
Also so many people have children and are not married that the term in many cases is redundant. Many people believe that because the parents live together and are a family unit that does not apply that their children.
Also as unwed parents are now in all walks of life that people feel to use the term for a professional family is totally inappropriate. I have known factory manages, teachers etc all with children out of wedlock. The teacher continued to work until she went on maternity leave and returned to work afterwards there was no problem with the school the parents that she was not married and pregnant. I would go on to say she later married and is now expecting her third child but it does almost seem the norm that in most families the first child is born before the parents marry even if they go on to marry afterwards.
Time have changed and I fear not for the better.
“it is a term that so many people use just meaning that someone is being nasty, objectionable or in some cases just a pain in the neck.”
Similar fates have met other words, like “stupid” and “faggot,” which lose their special meaning through overuse. But that’s what keeps etymologists in business.