Harry wasn’t expecting to get any presents, so the idea of giving presents might not have occurred to him.
On his first Christmas at Hogwarts, Harry didn’t think he was going to get presents, he was just looking forward to the food and the festivities. Because of his low expectations of his own presents, he may have just dismissed the typical association of Christmas with presents, without ever thinking of the idea that he can give presents to others.
“On Christmas Eve, Harry went to bed looking forward to the next day for the food and the fun, but not expecting any presents at all. When he woke early next morning, however, the first thing he saw was a small pile of packages at the foot of his bed.
‘Happy Christmas,’ said Ron sleepily as Harry scrambled out of bed and pulled on his dressing-gown.
‘You too,’ said Harry. ‘Will you look at this? I’ve got some presents!’
‘What did you expect, turnips?’ said Ron, turning to his own pile, which was a lot bigger than Harry’s.”
- Harry Potter and the Philosopher's Stone, Chapter 12 (The Mirror of Erised)
It seems likely that Harry simply overlooked the idea of giving others presents, rather than making a conscious decision not to. He is close enough to Ron that he would likely want to give him something if he’d thought of it. He does give Ron the fifty-pence piece he gets from his aunt and uncle, because Ron was fascinated with it since Muggle money is rare and unusual to Ron.
“We received your message and enclose your Christmas present. From Uncle Vernon and Aunt Petunia. Sellotaped to the note was a fifty-pence piece.
‘That’s friendly,’ said Harry.
Ron was fascinated by the fifty pence.
‘Weird!’ he said. ‘What a shape! This is money?’
‘You can keep it,’ said Harry, laughing at how pleased Ron was.”
- Harry Potter and the Philosopher's Stone, Chapter 12 (The Mirror of Erised)
He was friends with Ron and wanted to be nice to him, he just probably hadn’t thought of actually buying anyone Christmas presents.