As someone who has worked at a "Project/Service" company for way too long, I wholeheartedly agree. It's a horrible way to build software and will drain your soul. Good software is both much more expensive and much more valuable than most people realize, and one contract or client is never enough to give it the attention it deserves. Your clients will wonder why your $200k custom software doesn't work like Excel / PowerBI / some other product with tens or hundreds of millions of dollars of investment. It will wear on you that you simply can't give your software the love it deserves solely on the tab of one single client.