There are other candidates but none of them has any real chance of winning.
And none of them are particularly great in the first place anyway.
The us electoral system discourages people from voting third party since there is no ranked voting or second runoff system for the president.
Some progressives think that reforming the voting system would make society significantly better but there really isn't any evidence for that, europe has much more democratic voting system but it's much poorer overall than USA.