Why's it so common to love other people's children but not your own?

I've seen it way too much in Pakistan. Idk bout other countries though. Parents will give everything for a kid who's not their own but won't give a shit about their own kid.

Like my nieces and nephews often come to our house and my mum and dad will show them so much love even if they're disrespectful and hurt them.

As a kid, I once told my mum that her answer on my homework was wrong, I got a slap and a whole ass lecture and a hungry night. My niece, i get it she's a kid, hit my mum hard on her nose and my mum's nose started bleeding yet my mum just kissed my niece, nothing else. I don't say that she should slap my niece but atleast something. Like wasn't I worthy of some love too?

The niece I'm talking about is one of my female cousin's daughter. The cousin and her sister always got attention from my parents. I was like 7 or younger, I asked my mum if I could sleep in the same room as her and dad, she said sure but when it was like 9 o clock, I wasn't asleep and she just left to go sleep with my cousin cuz she was scared. I get it, my cousins deserve love too but am I srsly that shitty? Like what do they have that I don't?

I asked my mum for a paratha last night cuz I hadn't eaten anything throughout the day, I got a lecture and a paratha that she slammed on my table. But when my cousins asked for food, my mum immediately went and cooked food for them, it was 1 AM, I asked for food at 7 PM.

A few years back when I was attached to my dad, I went to his friend's house with him and when his friend's son bullied me, my dad didn't care but when I told that kid to stop and I pushed him back like gently just enough to make some distance, I got a whole ass lecture and my dad wouldn't talk to me for months.

Thankfully, now I ain't attached to any of em. I do love em and all but why's it that Pakistani parents love other people's kids more than their own. They treat their own like they're some experiment while others like a poor person driving a rolls royce being very careful with it.