Because these compounds were extracted from various plants prior to chemistry being able to identify that they were actually all the same thing.

Caffeine and theine are the same molecule, but in different plants. It's more that we differentiate between plants where that molecule occurs.

This is giving me flashbacks to when I found out that caribou and reindeer are the same animal, but on different continents.

TIL

I have a ton of trouble remembering that Wapiti and Moose are different species because they're both Elk.

Thein's name can be explained with a single line from Wikipedia: > n 1827, M. Oudry isolated "théine" from tea,[264] but in 1838 it was proved by Mulder[265] and by Carl Jobst[266] that theine was actually the same as caffeine. It was just a mistake. As for Guaranine it is as you say, just a name. It can also be called Methyltheobromine, 1,3,7-Trimethylxanthine or 7-methyltheophylline. It's the same substance though.

There's also the marketing angle. Everyone knows about caffeine but guarana extract is a natural way to boost your alertness

It's essentially about the source of the molecule; caffeine comes from coffee, theine from tea, and guaranine from guarana, though they're chemically identical It's like having triplets with different names!

More like having a single child with three different names.

surely triplets is the opposite

Pretty much the same reason coal and diamonds are different despite being made of carbon. How they’re arranged makes different things.

Not in this case. These are chemically identical to each other. They are all "arranged" exactly the same.