That's what my Music History professor told us. Brahms wanted to preserve the classical music forms, particularly in symphonic music.
Brahms was a great admirer of Wagner, and one of his prized possessions was an autographed score of Wagner's Die Meistersinger. It was Bruckner that Brahms abhored.
I think Brahms perceived Bruckner's enthusiastic appreciation of Wagner as bordering on sycophantical. If I remember correctly, after one performance, Bruckner genuflected before Wagner.
Ives disliked any music he percieved as ‘feminine’.