Are you referring to 'falling on your sword', or 'accountability' in your response? Some of your examples are not equivalent to falling on their sword. Notably, going down with the ship is the opposite (in some ways), as it is 'fighting to the end to save the ship and it's people'.
If someone (going down the ship wise) doesn't get on a lifeboat when everyone else has already gotten off, then yeah it's probably more about avoiding actual accountability (aka having to stand and take responsibility/long term consequences).
Regarding Victimhood/Martyrdom, there are many apocryphal accounts and personal anecdotes one can throw out. You'll get stories anyone in senior leadership when a CEO gets pushed out, to [https://en.wikipedia.org/wiki/Ch%C5%ABshingura] (specifically Lord Asano), to Gnaeus Domitius Corbulo [https://en.wikipedia.org/wiki/Gnaeus_Domitius_Corbulo], and many others.
Sometimes folks want blood, and they won't be satisfied until they get it. And often someone either stupidly volunteers (actually), or gets 'volunteered' by their boss.
Also, how is killing yourself quickly and (relatively) painlessly after a military failure NOT the relatively easy way out - instead of say, dying while fighting the enemy to the death (probably horribly disfigured and maimed in the process), or dying in torture while not giving anything up, or dying while trying to save the ship and the other crew, or returning in shame and being a social outcast, or dying after being shamed in trial followed by an execution, etc.
Literally all those other options can seem a whole lot harder than a gladius through the solar plexus at the moment. Also, notably, sometimes folks had 'help' on that last bit, though rarely was it featured prominently in the PR.
Seppuku - similar. Rather than 'living with dishonor' (aka being outcast from a insular and all encompassing society), or having to stand trial and defend yourself and getting shamed then executed anyway, etc. it's killing yourself 'with honor', so your family doesn't get their benefits taken and similarly outcast (as badly). Seppuku generally involves the second beheaded the person before they've had a chance to suffer much too, though there have been famous 'mistakes' made at times.
It also could be ordered by the Daimyo, Shogun, etc. and it was pretty common (from accounts at the time) for folks to be thrown under the bus and ordered to commit it if they didn't succeed at what the lord had ordered them to do or were just being inconvenient to the narrative. Including significant 'help' from seconds. Which is, well, pretty much the example of a scapegoat.