The problem is that dominant crypto assets keep changing. It was unthinkable that Bitcoin would become obsolete a few years ago, but it now seems like an entirely possible outcome. Ethereum is all the hype now, but it has got a lot of flaws and it will quickly be replaced once something better comes. Litecoin has always been just a gimmick. Monero was the only noteworthy (no pun intended) cryptonote coin, but Bytecoin has done its comeback and could reclaim the title of dominant cryptonote coin. Meanwhile Zcash could make both totally irrelevant. Or perhaps not. It's a constantly moving space. Maintaining a profitable portfolio requires a constant monitoring of the market. Not quite the low risk fire-and-forget approach the ideal retirement porfolio typically looks like.