He does not say a reason, and it’s not clear that he means there’s a minhag not to, just that l’ma’aseh they didn’t. I think he may mean like the Biur Halachah that it’s not a requirement. He seems to be showing only that we don’t pasken like those Rishonim who do require it.
http://beta.hebrewbooks.org/pdfpager.aspx?req=7705&st=&pgnum=365