Because nobody would use those chips for new projects. Legacy chips need legacy tools and run legacy software.
Moreover, embedded development is conservative by nature and I know a lot of teams which prefers to run projects on known hardware when possible, even if we have to suffer of the tooling.
Also, don't forget the licencing. We already have to downgrade our targeted platform because we couldn't afford to pay the whole tooling where OSS was only compatible with the previous version.