Is there even any reason the world needs more than 1 cryptocurrency? I know there are dozens (hundreds?), but they all effectively do the same thing, right? Allow decentralized currency that can be used for legal and illegal transactions.
Cryptocurrencies are tech products, various projects try various ideas. You'll have the initial blockchain idea from bitcoin, the privacy blockchain from monero, the programming contracts from ethereum, the decentralized exchange from stellar, etc.
I'm perfectly fine with that, I prefer to see people create new projects to test new ideas rather than to hear them complain bitcoin is not doing what they want.
* BCH as a fixed coin limit at 21 million. XMR has a tail emission so the coin supply will always increase
* BCH has a POW backed by ASICs and XMR has been doing all they can to brick existing ASICs and keep the mining on CPUs and GPUs
* BCH prioritizes scaling on-chain aggressively while XMR has more hope on second layer solutions
* BCH allows more script functionality (for example allowing you to store Twitter message, see memo.cash) while XMR disallows all that
* BCH has a transparent blockchain where all transactions can be traced while XMR tries to shield all senders and receivers
Of course other coins can make other trade-offs. Ethereum for example explores the extreme end of scripts on-chain, even having a Turing complete scripting language. Other coins are experimenting with alternatives to mining like proof-of-stake (POS).
Etc...
The vast majority of existing cryptocurrencies are just copies of others, or just sit atop Ethereum. Those will certainly end up being worthless or nearly so. That doesn't require that all future cryptocurrencies will necessarily meet the same fate.
We also don't need 10 different messaging apps.