https://www.nytimes.com/2024/02/25/world/europe/cia-ukraine-...
The first Kerch Bridge attempt was only a partial success. Traffic continued almost the next day. The second attempt was a complete failure. For the refineries, Ukraine uses at least GPS.
The sail boat theory is plausible from diving standpoint, but they allegedly installed explosives on NS-1 and NS-2 sites that were at least 100km apart, within 10 hours, with no decompression equipment. If they can do that, why do they repeatedly fail at Kerch Bridge?
The bridge is approximately 3km long or so, which makes it relatively easy to maintain a continuous 24/7 armed presence to prevent sabotage. An underwater pipeline is a 1200km stretch mostly in other international territory that is hard to protect. Definitely much easier to blow up a pipeline than it is to blow up a bridge.