Explanation: While the systems of Japanese and European feudalism are often compared, there are some major differences. One interesting one is the prospect of capture in wartime. In European feudalism, high nobility were almost always captured when possible. Since, by law, war did not abrogate feudal rights, a family on the losing end of a war would only lose some of their wealth and prestige, and so be able to still pay a generous ransom - which is generally preferred to a severed head!
The reasons for this are complex, but at least in part boil down to the very 'regional' system of peoples and feudal law cultivated. You can take a week's march and pass through seven languages in a single feudal polity. Count Dickweed might be a traitor, but unless he has ZERO justification for his rebellion, any serious punishment is going to make all of your other vassals - who command the loyalty of THEIR very particular regions which they insist have special legal codes - nervously eying up other lords to swear fealty to. There's no equivalent 'option' to just install whomever in power - some notable overthrows involving ethnic replacement of the elite exempted (Norman conquest of England, Baltic Crusades). The centralized authority doesn't have the power to hold all those lands by force, and so needs the extensive client systems of local (or at least long-tenure) notables to keep the peace.
In Japan, on the other hand, the system was very much predicated on personal service and loyalty. Regions of Japan are different, but generally sharing in a common culture, legal system, language, etc, giving most intrafeudal Japanese wars the mien of a civil war. For this reason, replacement, wholesale, of noble families was much more viable - who can trust a rebel, after all? And if the foe was not a rebel but a peer's vassal, then the thinking becomes "If he is a loyal man, he will never betray his lord and any claim of him laying down his arms in contravention of his lord's orders cannot be trusted. If he is a disloyal man, he cannot be trusted. In either case, I am safer with him dead than alive."
For this reason, while both common soldiers and samurai are recorded as being captured, and then ransomed (or sold as slaves if they can't pay), the commanders of an opposing noble force, even when they themselves negotiate a surrender for their troops, are often killed. Can't trust 'em no more!
Not only that, but the lack of consistency of noble ransom also meant that ransom was less lucrative. So it was more likely even for lower-ranking samurai that the enemy might just do the cost-benefit analysis of keeping you alive as a prisoner and figure... well, you aren't worth the rice to feed you.