This is the best answer posted in this thread as of the moment:
If everyone create their own currency and doesn't got a good features then it will be a dead coin, because the only one using it is only yourself, it is easy to create your own currency but it's hard to convince other to believe and used your coin, even if there are already people using your coin you still need to dedicate your time to make improvements and introduce your coin, so creating one coin won't make you less motivated
In addition to the post quoted above, if everyone creates their own currency and if all of it got good features to showcase, then obviously the ones that will have their own value is only the cream of the crop. The one that will have the greatest value as a currency is the coin that have multiple real world use cases(and because of the same reason btc still dominates the market). For this same reason, someone will still be motivated to work in different fields.