I read all of that and other resources online and still couldn't understand why the hell we need to build that and especially in south pole antartica
Why the pole specifically? You could probably build a second IceCube 100 miles away, but how are you going to get that materials there? Pole has a skiway for large aircraft and infrastructure to house a large number of people. The traverse (SPoT) only became operational near the end of construction - the initial holes were drilled in 2005 and almost everything had to be flown in.
Telescope In The Ice does a great job of explaining the history and science behind the experiment.
I'm personally very happy that we're still funding science that isn't obviously monetised.
The reason for Antarctica is that it's the only place you find cubic kilometres of stable ice that doesn't drift around.
All of it was driven by a flood of experimental results that were not compatible with classical physics.
See "Ultra Violet Catastrophe" in black body radiation, photo effect.
Planck famously performed curve fitting on the black body spectrum and only afterwards found the theoretical foundation for the function that fit the data.
I'm actually not sure exactly what "they" is in this sentence.
I know about the Ultraviolet catastrophe, but that's cherry-picking.
Dirac predicted the Positron before it was discovered.
Quantum entanglement was predicted by Einstein, Podolsky and Rosen before it was shown ("Spooky action at a distance")
Black Holes and Gravitational waves were both predicted before they were detected.
Einstein predicted time dilation before it was detected.
Szilard predicted chain reactions in Nuclear fission before they were demonstrated.
And probably most pertinent to this discussion, Pauli predicted Neutrinos before they were detected.
Half of the list above are critical for GPS, energy, semiconductor research and many other fundamental technologies of the modern age. They were researched and predicted without any thought of a "monetisable" product.
Because of the experimental result of missing energy in the beta radiation spectrum.
Bone of these were "pure thought experiments" as you describe. Many were side effects, new predictions of theories to address other experimental results, but none of them happened in isolation.
You simply don't make predictions about the real world in "pure thought experiments".
1: Ice-mass that isn't contaminated by atomic testing fallout (if the ice has been there since the 40s it's without radioactive waste (faschinating to read about how WW2 wrecks is a prime resource of steel since it's a huge amount of steel without trace amounts of radionucletiods from testing fallout).
2: No current interference (nuclear power, radiowaves,etc) creating possible test uncertainties.
3: I'm sure there are other reasons
The negative naturally is cost, but since the expriment succeeded it will probably be useful for any attempts to send robots or even humanity into space beyond the solar system.
https://en.wikipedia.org/wiki/Sudbury_Neutrino_Observatory
https://en.wikipedia.org/wiki/SNO+
https://en.wikipedia.org/wiki/Super-Kamiokande
There's a weird overlap in engineering and physics disciplines between the hard engineering/business practices of the mining industry, and particle physics.
The US has a research station at Summit Station Greenland but compared to South Pole, it's spartan (like, the first time I went there, I slept in a tent because of lack of hard-sided berthing, but then a Polar bear came a few years later and now hard-sided berthing is required). There are longer-term plans to improve the station in Greenland but we'll see.