Screenrant explains the change and connections, suggesting that Cyborg fits thematically in couple of ways, is connected to Doom Patrol in a secondary way, and believes his presence will help attract viewers.
...While Victor Stone was never a part of the Doom Patrol in any comic
book series, he would be a perfect fit for the team thematically.
Every member of the classic Doom Patrol had their life endangered by a
horrible accident and was saved only by an experimental treatment
conceived by Dr. Niles Caulder. It could be argued, however, that
death would have been preferable to Dr. Caulder's cures, which left
his patients as something both more and less than human and often
wishing that they had been allowed to die. This was the exact same
state that young Victor Stone was in immediately following his
father's efforts to save his life.
Though Cyborg was created nearly two decades after the first Doom
Patrol comics were published, his origin story fit the same tragic
mold as Elasti-Woman and Negative Man. The body horror parallels are
particularly strong between Cyborg and Robotman, whose brain was
transplanted into a super-strong and almost unbreakable robot body
that was also incapable of smelling, tasting or any fine sense of
touch. Given that, it is surprising that a connection between Cyborg
and the Doom Patrol has never been established before now. This seems
particularly strange given that Cyborg's closest friend in the comics,
Beast Boy, was a member of the Doom Patrol before he joined the New
Beyond the thematic connections, Cyborg's induction into the Doom
Patrol will also serve to attract casual comics fans to the new series
and offer them an accessible frame of reference.
And to help confirm Screenrant's assessment, actor Joivain Wade (Cyborg) basically says nearly the same thing, but with the notion that *maybe this is how Cyborg becomes the character he is in Teen Titans, *should that be DC TV series' plan...
"Every single person in the Doom Patrol has gone through traumatic,
unfortunate events which have given them some kind of dysfunction or
disability," Wade says. "Vic has turned his into something good,
whereas the rest of the guys are essentially learning how to turn
theirs into something good. But when it comes to him learning and
growing and becoming who he's meant to be, who better to learn from
than a bunch of characters who have also gone through similar things?
It's been a greater playground for him to be discovering and learning
about himself to then be ready to join the Titans when the DCU decides
to do that."