Why not? there are too many good altcoins out there and I believe that at least 10% of them have a good future. 1% of them can even beat and replace bitcoin. Mark my words. Look at ethereum and litecoin, as well as lumens. Their market caps are extremely big right now
There are a lot of good coins out there but not one that can surpass bitcoin and if that coin does not appear soon then I think bitcoin is going to remain the top cryptocurrency for a long time because the advantage bitcoin has by being the first crypto ever is getting larger by the day.