Why would you forget a seed with a million worth of Bitcoin in it?
I don't have that much but I will never let my seed be forgotten or lost, the same with my private key. Either way, if that is transacted, it will be a talk of the community. It is true that Bitcoin is volatile, that it would dump and pump in a certain time but with a lot of people supporting cryptocurrency, I don't think it is that bad. People are taking advantage of those movements to earn some profit in the long run.
Not all of the investors of bitcoin or crypto currency as a whole are like you. There are a lot of incidents that investors lost their key, their files, showed their private key to everyone, or sent their bitcoins into the void. Incidents happen but I do agree that this is not the reason for these people to avoid it, there would be other reason.
That would be a different scenario if they have a million in that wallet.
I don't think that they would just let it in there without doing anything to take care of it. I know that there are incidents like that happened in the past but with the value of Bitcoin right now, investors especially holders have their safety measures and I don't think it would be the same as in the past. Right now, one of the most reasons why Bitcoin is lost is that because they are accidentally showing their private keys or maybe because of scams and hacks that is happening.