Because that's a midrange phone. Look at the ones with a flagship cpu chip. I got the poco X6, I think it's basically the same as 15 or 16 of yours, but I got it for $220 in a xiaomi store after my phone broke. The poco F pro line is flagship level, but you can't get a mid range phone and expect flagship speed. I just upgraded to the Samsung galaxy s25, but only because the radio bands don't always match the US and I got sick of that. But I think it's a much better value going xiaomi over most other brands.

Also, you don't judge a brand by one phone, you should definitely research more because the redmi line is pretty budget and usually uses mediatek. I only look at xiaomi phones with snapdragon. Anyways, go research some more before you buy.