Just like anyone can copy bitcoins code and create their own coin, bitcoin can do the same thing to competitor coin. Bitcoin being the first, largest, most secure, most well known makes it the most valuable. This value puts bitcoin in the unique position to either innovate or adapt it's way out of the problem and survive on the other side. Small coins have to innovate to become a serious competitor to bitcoin whereas the bitcoin can allow a little time for the new technology to prove its self at greater scales and then adopt that technology if it hasn't found a way to innovate a better or at least competing technology. Bitcoin has been copied, forked, and attacked in almost every way possible in the last 10 years and has never given up the top spot. When the true competitor does emerge it will not be overnight and with bitcoin in the top spot it will have the most time to attempt innovation before possibly adapting the new tech in one form or another into bitcoin and preserve the network effect that has been achieved. None of the other coins have solved all of bitcoins problems so far so it's a little unrealistic to think bitcoin would have solved them all yet either so the "why bitcoin" is that based on the last 10years bitcoin has the best track record of any crypto at solving the cryptocurrency puzzle so far and based on value compared to its peers people expect that track record to continue.