Who's your 'they'? The only formal news reports I've seen just sheepishly say 'erm, it looks like 'someone' has sabotaged them' (I expect a memo will go round telling them to get on message and at least semi-officially implicate the Russians over the next 48 hours - although so far the mouthpieces I've seen are saying 'shitty Russian construction and maintenance' which is funny on multiple levels one being it was also built, and maintained, by Germans). Even (UK based!) tabloid commenters I've seen so far can see past this BS...
There's no reason for Russia to destroy the nordstream pipes (by entering Danish waters to do it to boot) outside the realm of bizarro 5-D chess conspiracies. It already controlls the gas flow, it could dismantle the pipes in its own territory (in case it wanted to repair them later) if it wanted to more permanently inactivate/depressurize them, and although Germany is very unlikely to defy the USA and start asking for more gas again the mere presence of the pipes creates a certain pressure/temptation to do so (especially if the shit really hits the fan for German business & manufacturing) which is a very nice carrot for Russia to keep hold of and dangle over them.
Diving undersea in Danish waters to destroy cables that are German property to make sure Germany (and Europe) is good an properly screwed is within the capabilities and the interests of one state only, and as it happens the loose-lipped Head of that state openly said they were gonna do this, months ago.
Just another act of terrorism by Great Satan USA against Europeans, nothing to see here...