Different budgets (in a lot of companies they don't have to do paperwork for a project that fits in the assigned budget, but monthly contracts have to be improved higher up and with the IT dep etc) and one doesn’t exclude the other; once I built it for that company I can recreate it and try to sell if I believe it's worth it. My first SaaS company actually was created (in 2001) when one of my enterprise clients said I was allowed to not only sell the solution we built for them but they would actually encourage their competitors to use it so they get new features without having to start a new project themselves. But we kept selling custom/from scratch implementations as well because some companies simply want to own things. The company still exists and sells the same product (very much changed over the years). Was built in Java.