I remember when btc was at 15K, many of them said they would wait for it to drop to 12K before buying,

I think the issue here is not really them wishing, it is because they were just afraid to invest in something with 15k which is a bad mentality. They don't have an investor mind. An investor mind will risk it even if it's 100k.

The fear of losing will not make some people take the risk of investing but now they see that there's profit instead of loss so they are wishing that they had invested early or so.

Profit is not for everyone wishers, profit is for risk takers.