The Polish prime minister immediately called "sabotage" and fingered Russia, while everyone else is still saying "it could be sabotage but we need to investigate first".
Russia wants the taps capable of being turned ON at their discretion, not permanently broken. This hurts their bargaining position in a big way because they've just lost their biggest source of leverage against Germany.
Poland opened a new pipeline to Norway on the same day as the leaks appeared, so there was lots of Polish activity in the waters.
Poland doesn't receive gas via Nordstream, so damaging it doesn't hurt them in any way.
Poland is Ukraine's most ardent supporter in Europe, often leading the vanguard of actions to support Ukraine. They'd have a strong motive to ensure that the rest of Europe doesn't waver in its commitment to keep the Russian taps off.
It could be argued that since Europe has already decided to never turn on Nordstream again, the fallout from such an act of sabotage is minimal.