Bitcoin isn't software, it's a protocol like email.
Google didn't invent their own email protocol when they developed gmail - infact gmail would be useless if it used it's own protocol because you would only be able to communicate with other gmail users. The BBC would not be able to send an email to a gmail user from an @BBC.com email address.
Protocols are very resilient - even when they become outdated because they are just protocols without a hidden agenda.