That’s because Dark Phoenix is expected to be the swan song for this current iteration and continuity of the X-Men onscreen, now that Disney has bought 21st Century Fox, and the belief is that the mutants will be rebooted down the line in the MCU.
Despite her willingness to at least consider playing Jean Grey again, it would be extremely surprising if someone were to give Famke Janssen that call.
Even Sophie Turner doesn’t seem long for the role.