Low platelets 90-130k, saw hematologist, blood tested for cancer/disorders. Liver/kidney/immune tests ok. Can platelets just be low for no reason?

Yes/No. One condition that comes to mind is ITP (Idiopathic Thrombocytopenic Purpura). A good hematologist can check you for this condition which sooner or later requires treatment as platelets keep going down slowly. You should have your Platelet count checked every few months and enlist(tabulate counts so that you can see if there is a trend downwards. If the count is <100,000 then you likely have ITP.