Why did Harry get his letter by owl instead of from someone from Hogwarts?

Question

We know that Muggle-borns get someone from Hogwarts with their acceptance letter to explain everything to their parents.

Q: How are Muggle parents convinced to let their kids go to Hogwarts, a strange place they never heard of before; and wouldn’t they think it was a practical joke?

A: In the case of Muggle parents, special messengers are sent to explain everything to them. But don’t forget that they will have noticed that there’s something strange about their child for the previous ten years, so it won’t come as a complete bolt from the blue.
_{J.K. Rowling (2004)}

‘It’s real for us,’ said Snape. ‘Not for her. But we’ll get the letter, you and me.’
‘And will it really come by owl?’ Lily whispered.
‘Normally,’ said Snape. ‘But you’re Muggle-born, so someone from the school will have to come and explain to your parents.’
_{Deathly Hallows: Chapter 33 - The Prince's Tale}

Since Harry was given into the care of two Muggles, how come they got pelted with letters instead of having someone from Hogwarts coming to explain it all? Had Dudley been a wizard, he would have been Muggle-born, so it seems that Harry should have gotten the same treatment since he was raised in the same household. Is there a valid in-universe reason for this? Or is it simply a plot device?

Answer 1

Since Harry was from a wizard family, the Ministry would presume his guardians, knowing about the magical world, would have told him.

Hogwarts sends officials to notify wizards born to Muggles, who would not have known about the wizarding world prior to their visit. Harry had two wizard parents, and the Dursleys did know about the magical world. The Ministry, and even Dumbledore, would have likely presumed that the Dursleys would have told him before he was old enough to go to Hogwarts.

Hagrid certainly expected Harry to know about the wizarding world when he was sent to get Harry from the Dursleys.

“Call me Hagrid,’ he said, ‘everyone does. An’ like I told yeh, I’m Keeper of Keys at Hogwarts – yeh’ll know all about Hogwarts, o’ course.’

‘Er – no,’ said Harry.
_{^{- Harry Potter and the Philosopher's Stone, Chapter 4 (The Keeper of the Keys)}}

Hagrid is angry with the Dursleys because they never told Harry about the wizarding world or that he was a wizard. He knows that Dumbledore left the Dursleys a letter explaining everything to them and both he and Dumbledore expected that the Dursleys would have told Harry what was in the letter.

“Yeh don’ know what yeh are?’ he said finally.

Uncle Vernon suddenly found his voice. ‘Stop!’ he commanded. ‘Stop right there, sir! I forbid you to tell the boy anything!’ A braver man than Vernon Dursley would have quailed under the furious look Hagrid now gave him; when Hagrid spoke, his every syllable trembled with rage.

‘You never told him? Never told him what was in the letter Dumbledore left fer him? I was there! I saw Dumbledore leave it, Dursley! An’ you’ve kept it from him all these years?’
_{^{- Harry Potter and the Philosopher's Stone, Chapter 4 (The Keeper of the Keys)}}

Answer 2

First of all, remember that this is a Hogwarts based rule. There is no ministry provision that all muggleborn wizards have to have a Hogwarts representative show up at their house, it is simply helpful. Just imagine if (prior to the books existing), you had gotten a letter telling you that you had been accepted to a magic school, Turkey Liver. You would throw that letter in the trash as spam.

Moreover, it is helpful to have a proper wizard show up to explain important laws, like the statute of secrecy. Not to mention being able to prove that magic is real. They could do a quick bit of magic to prove that magic is completely real, which would encourage the parents to accept the offer, and let their kids go to Hogwarts.

So, since this is completely up to the Headmaster's discretion, that means that Dumbledore gets to call the shots on who gets a proper visit. He knows for absolute fact that the Dursleys know about magic. Petunia had a witch for a sister and even asked Dumbledore to allow her to go to Hogwarts. So, she, at least, knows Hogwarts exists and knows what it is. Dumbledore may have been naive enough to believe she would simply let Harry go to school, but I don't believe that is the whole story.

Remember the beginning of the Half-Blood Prince, Dumbledore knows what kind of people they are, and teases them by use of magic, (the bouncing mead). Dumbledore wanted to pay them back for the abuse they gave Harry. It is altogether possible that Dumbledore knew Harry would never receive the letters and used them to mess with the Dursleys. After all, it is not exactly common courtesy to fill someone's whole house with letters, having the letters pour in through every euroffice of the house. Nor is it nice to chase the Dursleys half-way across Britain, having every hotel stocked with three or four letters. Given Dumbledore's nature, I assume he is having a private laugh, at the Dursleys expense, and I assume he always intended for Hagrid to give Harry his first tour of the magical world.