Firstly, it's a rush job. The collective West has run out of road. The so-called counter-offensive has failed, the first Kerch attack failed, they are without air defence being mauled on the big screen. Back in the US, Donald Trump is still a force to be reckoned with.
Secondly, they have no wiggle room. Every manoeuvre on their part is easily, even swashbucklingly, repelled by the Russians. The British neocons and their Polish lapdogs either act now or expect more humiliation as their military might is destroyed by Russia on the big screen. They have a small window of opportunity. Timing is everything.
Thirdly, the collective West has not honoured any of its commitments to Russia. Putin has specifically called it a terrorist attack since the bridge has been a civilian corridor for many months, suggesting a secret agreement with the West/Kiev, perhaps as part of the grain deal. https://simplicius76.substack.com/p/kerch-bridge-deja-vu-breakdown Ukraine had been using the 'green' shipping lanes to ship arms, which was also prohibited under the deal. Russia was to have the SWIFT system returned for a major bank financing fertilizer exports - that didn't happen either.
The haste with which they have had to act, having failed to gain an advantage makes them very, very dangerous. They see this moment, the ending of the grain deal, as their only option for a scare event or other means of gaining the upper hand. That's why the second Kerch Bridge attack is a big deal.
Russia responded to the terrorist attack on Kerch bridge attack by bombing Odessa and terminating the humanitarian corridor though the northern Black Sea.
Putin stating that Russia will respond militarily
https://archive.ph/w2oPp#selection-759.0-759.81
More excellent articles and further extrapolation in the comments here
https://greatawakening.win/p/16bj0cSQhW/why-the-second-kerch-bridge-atta/