There are coins that do the same thing as bitcoin but they haven't been around as long and thus aren't as trusted. Bitcoin got there first and will likely always be on top, but transaction tokens will likely always exist and attempt to compete. I like to think of Bitcoin as Coke and Ethereum as Pepsi, while the other altcoins are the store brands or lesser known brands like RC cola. There's room for all of them to exist. They can be rivals, but all support the market at the same time.