ABC Entertainment cancelled Roseanne due to her tweeting the following in reference to Valerie Jarrett:

muslim brotherhood & planet of the apes had a baby=vj

The situation escalated with Reverend Al Sharpton demanding action from ABC:

The comparison by Rosanne Barr on ABC of Former Obama aide, Valerie Jarrett to an APE is racist and inexcusable. ABC must take action NOW!

Quickly after Wanda Skyes announced she wont be returning to the show:

I will not be returning to @RoseanneOnABC.

And in the end Bob Iger conceding ABC didn't really have a choice:

There was only one thing to do here, and that was the right thing.

The show's tenth season (after a 20 year hiatus) was a bit unusual due to its 'conservative' nature and often going against the grain to the point that the main character was a Trump supporter. The success of the season was remarkable in today's days of declining television with 'the highest rated Tuesday entertainment telecast in 6 years among adults 18–49 and television's highest rated comedy telecast on any night in 3.5 years, since The Big Bang Theory in September 2014.' (link)

On one hand the quick cancellation surprises me due to massive success of the reboot, but on the other hand I always had a feeling like there is a big tension tension between ABC and Roseannes never ending tweets that were at times pretty controversial.