There are mainly two reasons why Bitcoin remains as the most popular crypto-currency out there. These are:
1. Bitcoin was the original crypto-currency. Other alts such as ETH and BCH are at least partially based on Bitcoin.
2. Most of the trading for the other crypto-currencies (perhaps with the exception of BCH) comes from trading versus BTC. Alt vs fiat trade volumes are quite low.
I think bitcoin is totally different than any other crypto because in past there where some crypto in market but all of them were full of problem because bitcoin is now here to help us and bitcoin make a life of people comfortable and it facilitate life as well because bitcoin price is very high and its very safe and sound for its users you can invest here as much as you can and also you can do daily trade and I will give you your profit on time thats why its so popular.