I had a baby red winged black bird found it on the floor .took it home an fed it boiled egg yokk and baby food mixed together 5 days later it died can someone tell me why?? He was doing so good by the way he was a flegding

Sadly most people cannot successfully raise a wild bird. The amount they need to feed, what they need to eat, etc. etc. isn't something most people can successfully provide.

Whatever other problems the baby may have had, it/they were aggravated by the stress birds experience when removed from their natural surroundings. Another reason it is hard to rehab injured birds for most people.