my question is that why can't they last and be like Bitcoin and what does it take for this unstable cryptocurrencies to be like Bitcoin.
I'll be glad to get responds to add to my knowledge concerning this . Thank you
First of all, don't forget about Ethereum. This altcoin is more popular today, or at least its blockchain, as it is more convenient for developers to make up their product exactly on this platform.
Secondly, you are not right that Bitcoin is fast. Compared to altcoins and even to some payment systems like Visa, it is extremely slow. So altcoins can replace Bitcoin in terms of cheapness and speed.