In Star Trek: Picard, the search for Doctor Bruce Maddox is an important plotline for the first half of the first season. When he is ultimately found, he is no longer being played by Brian Brophy, who played him in The Next Generation's second season episode "The Measure of a Man," but instead a different actor. Brophy is still working, it seems, if one looks at his IMdB. The same applies for Icheb, who played a somewhat important role in the last seasons of Voyager. Manu Itriyami expressed his willingness to return to the role, so why wasn't he brought back?
Manu Intiraymi / Icheb.
Manu Intiraymi's recent behaviour (on twitter and elsewhere) in mocking Trek actor Anthony Rapp's allegations that he was assaulted by Kevin Spacey and then expressing vocal support for Spacey almost certainly cost him any chance of returning to play Icheb. Notably he's also been excluded from various 'official' Star Trek conferences and appearances.
They’ve kind of blacklisted me from cons too. I don’t get invited anymore. I’m sorry. I will be in Edinburgh Comiccon in April 11 and 12. Maybe my last show
I’m not sure why I wasn’t invited back on the show, I was referring to the Star Trek personal appearance scene. Fandom, conventions, Cruises, dinners etc...I’ve been what amounts to kicked out of that scene, unfortunately. I liked hanging with the fans.
Brian Brophy / Bruce Maddox
Brophy appears to have intentionally retired from acting and is working full time now as the Director of Theatre Arts at CalTech. Since 2004 his only acting credits are a 2014 short film directed by some of his students from CSULA and a couple of cameo appearances in Southland in 2009 and 2011. I suspect if we went digging, we'd find that these were also personal favours to a former student. Other than that he has no acting credits but plenty of directing credits.
I would assume the Casting Director for Picard made some general enquiries about Brophy's interest in playing the role (he seems to be in the good books with Paramount as far as I can tell) and was politely rebuffed.