I don’t wanna get too tinfoil-hat here, but I dunno… something feels off about this whole thing. What could it be? Did Charles ask for too much money? Did Charles want to go union if he wasn’t already? Did he actually want to retire? Everything Charles said publicly in the past few years makes me think this was not his call.
It could honestly be that he just decided to retire and he changed his mind about playing Mario for the rest of his life. I guess we’ll never know.
I'm going to quote this post, despite it having been quoted several times before, because I really need to highlight what it is you're insinuating here.
Companies have dropped voice actors before. Companies have dumped voice actors before, unceremoniously and acrimoniously. Many times, VA's have voiced their displeasure over this.
Nintendo didn't dump Martinet. They made a formal announcement, thanking him for his performances over the years.
They announced at the same time that they're still retaining him as a Mario brand ambassador going forward: anyone who has followed his career knows that this is something he was already involved in. Not just fan cons or signings, he would go to official Nintendo events and talk about Mario and Nintendo projects on stage, often in multiple languages as the man is fluent in multiple languages.
On top of that, all parties involved release a video where, q'uelle surprise, they state how happy they are with this new development. Martinet is still getting paid, still getting to do work he by all accounts enjoys, and Nintendo get to keep a good relationship with one of their most prominent voice actors.
They could not be more public about what they're doing. This whole "I dunno guys, something is reeeaaaally fishy about this" line is just baseless conjecture that flies in the face of observable facts: an elderly voice actor is passing on his most famous role to a younger voice actor after decades doing the voice (and voice acting is murder on your vocal chords), he's getting to keep doing parts of the job he still enjoys, and Nintendo is happy to keep paying him to do so.
You don't need to be Poirot to realize there really isn't much mystery here