The US were not thrilled about it when it was being constructed, obviously, but this was normal tensions towards Russia, prescient in the end but here we are.
There were several countries arguably interested in getting rid of that pipeline (Ukraine, Poland, the US), but Ukraine wanted it the most, had easy access, and there's no need to overcomplicate internet theories.
No, "normal" humans don't dive to 80m deep, where the explosion occurred. Any diver, whether professional or recreational (which is my case), will know about this. I don't have a (alternative) theory about this, I'm just stating facts. Well, the alternative theory, if we are speaking of divers, is that they had some very special equipment and were extremely skilled. It wasn't some random people, renting a random boat, renting random diving gear and buying random explosives ..
"The open-sea diving depth record was achieved in 1988 by a team of COMEX and French Navy divers who performed pipeline connection exercises at a depth of 534 metres (1,750 ft) in the Mediterranean Sea as part of the "Hydra 8" programme employing heliox and hydrox."
Sounds like 80 meters is cake walk for any modern naval institution.