Some of it may be to do with the perceived success of the early kings to bear those names. Although William I was no doubt successful, his son William Rufus was largely unpopular amongst his barons and the people at large, whilst his younger brother Henry I was instrumental in expanding and consolidating Anglo-Norman England, expanding into Wales and delineating and fortifying a border with Scotland, and was widely perceived to be a very effective king. Edward I is known for his widespread and significant legal reforms as well as his conquest of Wales and the mass construction of major castles. To adopt their royal name was to hope to adopt some measure of their success.

It's the same reason why the name Charles is a rare royal name: the first Charles was beheaded after losing the civil war.

Aside from the, very accurate, response above I'd add that some of this was just luck.

Henry I was a third son and never intended to become king. But after William Rufus died he was able to seize the crown while his older brother, Robert Curthose, was away on crusade (to be fair to Henry here, William I hated his son Robert and never wanted him to be king). But Henry I did name his own son William. But William Atheling tragically died on the White Ship and wasn't able to become king.

Henry's daughter, Matilda, named her son after her father. He became Henry II. King John named his son after his father, Henry II. He became Henry III. Henry III was obsessed with Edward the Confessor so he named his son the very English name Edward, which seemed ridiculous to the Norman nobles at the time but then the name became all the rage. Edward I named a son after himself. Edward II named a son after himself. (Edward III did too but Edward the Black Prince never became king.) Henry IV was a usurper and never intended to become king. His father, John of Gaunt, wasn't naming him thinking of his being in a line of kings (although certainly his own royal lineage was a part of it and it was in homage to them). Henry IV named a son after himself. Henry V named a son after himself.

Henry VI's mother, Catherine of Valois, had illegally remarried after his father had died. Her husband was a Welsh man who worked in her service, Owen Tudor. They had two children together. Edmund and Jasper Tudor. When Catherine died Henry VI hadn't known any of this and Owen feared for his life and his children's lives. Such things could mess up the succession and were frowned upon. But Henry VI was a good hearted person, albeit mentally ill, and welcomed his brothers and provided for them. Out of gratitude Edmund named his son Henry. Who became Henry VII. No one would have predicted that when he was born.

Edward IV was also not expected to become king when he was born (his father didn't assert their claim to the throne until Edward was an adult). But was surely named after the illustrious Edward III. Edward named a son after himself (who was crowned Edward V before being locked in the tower).

Henry VII named a son after himself, who would become Henry VIII. But Henry VIII wasn't supposed to be king. His older brother Arthur, to hearken back to those glory days in Camelot, was supposed to be king but died.

Long story short, some of the naming conventions were just the natural act of fathers or grandfathers having sons named after them. Some of it was idle fancy (Henry III happened to have a thing for Edward the Confessor). Some of it was pure dumb luck that these guys with these names ended up on the throne, at all.

Had William Rufus lived longer or had children or if William Atheling hadn't died maybe there would have been more Williams. Sons or grandsons, who never came to be, might have been named for those men. Had Robert Curthose actually been able to get the throne over Henry I maybe there would be some Roberts.

This is in addition to the true fact that children were named for people deemed to be a success, said above. Not in lieu of it.