Cryptocurrencies generally are considered an investment in the financial world though. The two things they are generally classed as are investments or a form of currency (in reality they are both but some people will class them as only one or the other). They certainly aren't a game though. Investing in them is uncertain so you could say investing in them is a "gamble" but something being uncertain / being a "gamble" is not the same as it being a game and cryptocurrencies do not meet the basic definition of a game.
You can also lose money on securities. Cryptocurrencies are a high risk, potentially high reward investment and investing in anything comes down to a risk-reward analysis, with term deposits and government bonds etc being low risk, real estate being about medium risk and shares and cryptocurrencies being regarded as high risk investments (cryptocurrencies more-so than shares but both are high risk investments). Higher risk investments have a higher risk of losing money but also typically have higher potential returns. That's where risk / reward analysis comes in, as well as whether an investor is risk-averse etc.
Posting on steem also doesn't have the risk that buying steem does. You are potentially wasting time there, not wasting money directly like you would if you spent money on steem and the value of steem falls.
It can be debatable if cryptocurrencies are investments or not (though the general concensus seems to be that they are an investment, albeit a high risk one), but they aren't a game. Being uncertain does not mean it is a game.