I saw one animated one Youtube once and it left me feeling kind of depressed, given that Zero basically slaughtered the entire cast of the classic series. Can't say that I blame Capcom for not wanting to release a game that features one of the two central characters of the franchise going forward committing a wholesale slaughter of lighthearted characters. The experience of controlling Zero in Mega Man X3 might be tainted somewhat by the knowledge that his badass energy sword had previously been used to bring Rock's mission of everlasting peace to a swift end.

My personal retcon is that X, despite being far more advanced than any other known robot (even Zero), is another prototype alone the lines of Blues. Rock had already exhibited behaviour indicative of his possessing the capacity for independent thought and action beyond what robots are supposed to be capable of prior to the end of the classic era (specifically, the ending of Mega Man 7). Dr. Light no doubt observed this unexpected change and started working on software and hardware that would allow Rock to cope with his development of genuine agency. But I also assume that Rock was like Dr. Light's surrogate son. Instead of risking Rock's wellbeing, he developed a new robot to serve as the prototype for robot designed to handle the stress and complexities of independent action.

The X series establishes that Dr. Light sealed X away while diagnostics were run on his system, but X wasn't the only one put away in long-term storage. A much more secure installation containing Rock was also created prior to Light's death, which may have also included the upload of Light's consciousness into a computer system that has long been speculated about by fans. Although Light does care about X, the capsules are a kind of two way street. X is provided with physical upgrades at the same time that software information is downloaded from his system to a secret location containing Rock. This data is used to asses how the robot closest to Rock in design copes with the experience of free will, particularly under conditions of intense stress. So intense was Light's desire to ensure that Rock emerged as healthy as possible that he even expanded the analysis by collecting data from Zero, a robot he no doubt detested for severely injuring/deactivating Rock at the end of the classic era.

I recall that Inafune was explicit that Rock and X are two separate robots. From the beginning of the X series through the end of the ZX games, X is the character who drives the story forward. (Particularly given the role of X in the Zero series). But given that Legends is in the same timeline, and that the central protagonist in those games definitely isn't X, who is he? He's the original Rock. Dr. Light wanted to make sure that Rock would be able to live out the rest of his existence in peace, both because of his battles against Wily and his final encounter with Zero. Rock Volnutt is the original Rock, finally who was finally released from his crystal storage unit when Light's consciousness/AI facsimile deemed the world sufficiently peaceful for the creation that he/it had long ago found stable enough to exist in the world in possession of free will.

Wow. That went on longer than I though. Maybe I should post this over at fan theories. Any thoughts on this idea over here in r/Megaman?