Nicotine often shows up in suggestions. On some people, quite high. It was included because we include everything we find studies for (including Round-Up!). Then I got a reader with ME/CFS who found that nicotine patches caused a major improvement. Then I saw someone mention that 30 years ago, smoking/nicotine was suggested by some MDs to stop UC’s Flares.
nicotine modulates the immune system, inhibits innate and acquired immunity and is used in treating many autoimmune diseases. It often stimulates the α7 receptor and causes an anti-inflammatory state in the body. This study is designed to evaluate the role of nicotine treatment on immune system. The results showed that nicotine affects many cells in immune system, alters the downstream intracellular mechanisms and changes lymphocytes polarization.Effect of Nicotine on Immune System Function 
Smoking tobacco is associated with a number of gastrointestinal disorders. In some, such as Crohn’s disease and peptic ulcer disease, it increases the risk of disease and has a detrimental effect on their course. In others, such as ulcerative colitis, it decreases the risk of disease and can have a favorable effect on disease course and severity.Mechanisms of Disease: nicotine—a review of its actions in the context of gastrointestinal disease 
Ulcerative colitis (UC) is predominantly a disease of non-smokers and treatment with transdermal nicotine improves symptoms in UC patients, whereas smoking seems to have a deleterious effect in patients with Crohn’s disease (CD).In-vivo effect of nicotine on cytokine production by human non-adherent mononuclear cells 
Anecdotal reports suggest that smoking may be beneficial for patients with inflammatory bowel disease (IBD) as nicotine may act through inflammatory mediators within the colonic mucosa….Moreover, concentrations of IL-1beta and IL-8 were significantly reduced in smokers with UC compared with nonsmokers with UC.The influence of cigarette smoking on cytokine levels in patients with inflammatory bowel disease 
In this relatively small study of patients with active Crohn’s colitis, 6 mg nicotine enemas appeared to be of clinical benefit in most patients. They were well tolerated and safe.Nicotine enemas for active Crohn’s colitis: an open pilot study 
It appears that smoking is bad for Crohn’s, but nicotine may be beneficial. Most studies are on smoking and not nicotine in isolation. IMHO, the suggestion of nicotine is probably a valid (and unusual) one.