I want to know why is only Bitcoin in the limelight I have someone that wants to invest in crypto but wants to invest in other coins he wants to know if other are same values as bitcoin and if other coins can be easily be exchanged or sell or for purchases.
Bitcoin is the first cryptocurrency ever created and other altcoins just follow the path of bitcoin, or I can say they failed to follow bitcoin. There is also some exception but nothing created so perfectly as bitcoin. As you said bitcoin is the base of cryptocurrency.
If your friend wants to invest in other coins it is better to have good research about the coin before investing money in them. Some of the coins have great potential but most of them are useless to me now.