You are not considering the inertia associated with network effects. The reason the internet has never upgraded from IPV4 to IPV6 is because too much hardware and software is dependent on IPV4. Bitcoin is like IPV4. It's just a base level protocol on which innovation can be layered.
The internet is in the process of upgrading from IPV4 to IPV6, and will continue. There's not much choice, given the limit on the IPV4 address space.
Bitcoin isn't like IPV4, because IPV4 wasn't the first. Bitcoin is like NCP (if my quick dip into wikipedia came up with the right acronym). NCP lasted about twelve years, it looks like. It was mostly used by geeks. Mainstream acceptance wasn't achieved until NCP was phased out in favor of TCP/IP.