Is the Harry Potter Universe Loveless? (or short on it)

While answering another question I mentioned the love protection spell from Harry's mom, which got me thinking, since this spell is so unique and no one understands it, does that mean not a single person in the entire history of wizards is known to have died for someone because of love and then have created a protection spell for that person? No parents, spouses or really close friends in the history of everything self-sacrificed for a loved one?

Did JKR create a loveless universe, where love was as miraculous and rare as the fact that Harry is the only person to survive Avada Kedavra?

Answer

UPDATE - I have found a much more definitive JKR answer as to why Lily’s protection was so unique:

TL;DR - because Lily was given an explicit choice.

ES: This is one of my burning questions since the third book - why did Voldemort offer Lily so many chances to live? Would he actually have let her live?
JKR: [silence] Can’t tell you. But he did offer, you’re absolutely right. Don’t you want to ask me why James’s death didn’t protect Lily and Harry? There’s your answer, you’ve just answered your own question, because she could have lived and chose to die. James was going to be killed anyway. Do you see what I mean? I’m not saying James wasn’t ready to; he died trying to protect his family but he was going to be murdered anyway.
…
MA: So no one - Voldemort or anyone using Avada Kedavra - ever gave someone a choice and then they took that option [to die] -

JKR: They may have been given a choice, but not in that particular way.
(Src: “The Leaky Cauldron and MuggleNet interview Joanne Kathleen Rowling: Part One,” The Leaky Cauldron, 16 July 2005)

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ORIGINAL ANSWER

The reason why the situation with Harry being protected this way being rare and unknown can be explained by 3 factors:

1. 
   

   Harry’s protection spell was VERY VERY specific:

   
   
   
   
   
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     Someone who loved him sacrificed their life to protect his

     
     
   
   
   • 
     

     The resulting spell was able to protect specifically against that attacker

     
     
   
   
   • 
     

     It is extremely likely that the 2 persons must be blood relations (which is why Dursley home is where Harry must live to be protected). - so, romantic love is out of the question.

     
     
   
   
   • 
     
     

     It’s also, as Jeff’s answer noted, logically sound to require that the target is someone defenseless, and can not fight back or escape after the first murder and before the attacker attacks them - meaning a small child as the case with Harry, or they are incapacitated by other attackers (which means they can’t survive due to not being protected from those OTHER attackers).

     
     
   
   
   
   

   As Jeff noted in his answer, given the small size of Wizarding community and relative infrequency of attempted murder therein, having all 4 of those conditions happen at the same time is likely not all that frequent of an occurrence.

   
   


2. 
   

   And even when/if it DOES happen, it’s likely to remain unknown. Harry’s case was special because:

   
   
   
   
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     He survived the first attack.

     
     
     
   
   
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     He didn’t escape from the second attack before it happened (meaning was a small child or incapacitated/restrained).

     
     
   
   
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     His attacker died from the Avad Kedavra rebounding. It’s not stated anywhere that the protection extended is explicitly designed to kill the attacker - the fact that the bounce hit Voldemort may very possibly have been a freak accident.

     
     
   
   
   • 
     

     There were no other attackers to finish the job.

     
     
   
   
   
   • 
     

     Due to the fact that his attempted murderer was a major league Bad Guy fighting a war, he was found by the rest of Order of Phoenix and the survival became known.

     
     
   
   
   
   

   In a random attempted murder situation, the protected person would either be hurt/killed by accomplices, or, if there were no accomplices and the person survived (and if a child didn’t starve to death afterwards), surely nobody would ever believed their word and take them as a lunatic (if they were an adult); or they wouldn’t even know what happened to tell them if they were a small child.

   
   


3. 
   

   And even when/if it DOES happen, and is known, it’s likely that very few people would know enough about ancient magic (like Dumbledore did) to actually correctly attribute the results - witness that everyone other than Dumbledore had no clue whatsoever as to why Harry survived both Voldemort’s attack and Quirrell’s attempt. This doesn’t necessarily address the rarity of people known to survive Avada Kedavra, but worth noting anyway.