Burps are 10x worse than farts.
There are 3 main reasons this is the case:
The smell. Farts have a wide variety of smells, from no smell at all, to room clearing foulness. They can smell like straight up diarrhea, or they can smell weirdly kind of good. Burps smell like puke, which is a much grosser smell. Or they just smell like whatever they were just eating, which is also disgusting and can ruin that food for you.
Burps are rude. Since a burp can always be suppressed or at the very least stifled with your hand, it’s rude to just let a burp rip in public. Plus most people can burp on command, so there is always a question if it was genuine or not. You can control much less about a fart. There’s either nothing you can do about them and you just have to fart, or they’re completely accidental. You can make an effort to hide it or leave the room if you know it’s gonna stink, but if you gotta fart, you gotta fart.
Farts are funnier. There is innate comedy built into a fart. Your friend accidentally loudly farts in a quiet place? Hilarious. You silently fart and are looking around to see who smells it first? Hilarious. Burps aren’t innately funny, in fact they are straight up disrespectful in some instances.
EDIT: One thing I forgot to add to point number 2, is that a burp is at face level. Somebody burping right by you is much more rude than farting right by you, because it’s right in your face.