https://www.metv.com/stories/fans-wrote-letters-of-protest-after-adam-cartwright-became-engaged-on-bonanza

Trouble in Bonanza...

Greene and Landon did not want Guy Williams to become a starring cast member, so having his character go off with Kathie Browne's was a convenient way to have him written out of the series.

That left Roberts' character unattached again. But the fans needn't have worried about Adam's romantic life. Roberts soon left Bonanza altogether.

If the fans had known how much Roberts wanted off the series, they wouldn't have bothered being concerned with Adam's romances.

Guess the producers were right in believing that the fans wouldn't like to see the Cartwright men married. Considering the show still airs to this day, they must have done something right.