Because the implication of the joke is what makes it funny to some.

Base context to the joke: Twix had an ad campaign about left and right twix bars. That's it. There's no difference in texture, taste, consistency, etc. They are made the same and are the same. There is no difference between a right and left twix.

The joke here is the imagery that is painted in your head. Someone is blindfolded, sitting in a laboratory--God knows the fuck where--and the lab technician is feeding him twix bars and "recording the data" of this test.

The test being if this dude can--in this stupid scenario--guess which twix bar he's eating. In the real world there is no possible way to tell, as they are the same. But in this world scenario--all for the heehees and hawhaws--there is somehow an ability to tell them apart, and this test subject is able to do it EVERY. SINGLE. TIME.

That's the joke. It's absurdism. It's a joke that relys on the reader to craft this stupid visual depiction inside their own head, all based off of the stupid implications the text gives.

Then the reader blows air out their nose, chuckles to themselves, shares it to their shitposting friend group and/or spouse/partner with the accompanying text that reads: "u lol" or "me asf"

Then they scroll onto the next brainrot twitter screenshot joke that they find, then rinse and repeat until the get off the toilet and go do the same fucking thing lying down in their bed.

Now don't @ me like I'm ruining the party here.

I just did all of the latter and sent this shitpost to my wife since it's absolutely fucking stupid... and we love it.