This was true up till now... but if Bitcoin will stay the king is more in doubt than ever. That was the point of the meme.
Are you sure about that? Are you willing to exchange your BTC for other coin? If you think another coin can take the lead away from BTC, then buy that one and become rich, but it's easier said than done.
Crypto is a way for people to become rich speculating like we've never seen before, it's bio/startups/penny stocks on steroids. Anyone could be holding the right coin that goes 100-1000% and become a millionaire, but they know that when they get those type of gains they are going back to BTC and they will sell a part to their fiat currency if they live in a stable country and leave the rest in BTC because BTC is becoming a solid gold alternative.