Rosanne never was a Conservative. Her character was a Hollywood parody of what they think Conservatives are (unwashed, dirt poor, racists). She herself, has always been a nasty racist.
She tried to run for president in 2012, as a socialist.
http://politicalticker.blogs.cnn.com/2012/08/10/roseanne-barr-dishes-on-why-shes-running-for-president/
She just hopped on the MAGA train as a publicity stunt. (unless she actually think that fits her socialist leanings).
Her actual politics aside for a moment... and yes, anyone who has been following her for the past few years know the only way to accurately describe her belief system inasmuch as such a system even exists is that she is a kook...
Roseanne was one of the highest-rated sitcoms to air in many years. Much of that came from conservatives in middle America, and ABC, home of such shows as
Modern Family, is known for nixing shows that are popular with that demographic (see
Last Man Standing). Not since the ill-fated
Bridget Loves Bernie has such a strong performer in the Nielsens been canned, and that was only because there were threats made against the network. You don't can a show doing that well unless something is seriously damaging (and her stupid comments in the past didn't stop the show from getting picked up) or the network wanted to get rid of the show all along but needed a reason to do so.
This will be spun as a shot against middle America, and it might well have been one. Or it might be a publicity stunt to see how many people call for it to be brought back.