My former GI Doctor was a protege of Dr. Shen who studied under him at Cleveland Clinic and spoke to him weekly, and he too shared a dim view of VSL#3 and other probiotics. He was also very dismissive of fecal implant therapy, calling it "nothing but a strong probiotic." VSL#3 was attempted in me more or less as "grudging due diligence", and it was utterly unsuccessful. It was also dangerous because when I stopped antibiotics cold to go on VSL#3, my condition would sharply worsen to the point where within 6 days I would be in a state where I was possible ER pre-admission. This was likely due to the absence of antibiotics rather than the presence of VSL#3, but I think some doctors are likely guarded about using it for this reason- that its lack of effectiveness in many or most patients exposes them to a worsening of their conditions.