Permit me to correct you, starting from the title you used, speaking of why Bitcoin is not crypto, which is wrong, because Bitcoin is a cryptocurrency. What you could have said is this: why Bitcoin cannot be considered an altcoin. This specifically explains your idea and the angle you're coming from.
Not back to Bitcoin and the aspect your discussion concentrates on, we can't have any other cryptocurrency that can fill the gap of Bitcoin, because it's all about privacy and everything works under a decentralized network, which we can learn from its whitepaper and also the history it makes right from inception.
You have just done what I was about doing, the op's topic and the body of his message is totally different, but you have just correct him or her and that is why it is always necessary for one to always go through the comments of others here after you have seen the topic or thread of anyone here so as to enable one to understand the particular topic very well, incase if there is any mistake from maybe From the topic or comments..
Just like someone have already said that cryptocurrency is a general name give to all the coin in the market,the only difference between the coins is how it structures are been built, like bitcoin is strongly build and it has no comparison with other coins and that makes it the best so far..