Aside from all the other answers, it would cost you millions to hire and onboard 146 qualified engineers. A place like Deloitte can drop them on your doorstep with a week's notice. They also have all the product design, strategy, and organization layers required to stand up the equivalent of mid-size enterprise from scratch really quickly and then tear it all back down a year later. I've worked in this business for smaller agencies and we could absolutely work miracles for stodgy organizations. My biggest account probably took in $20M all told and I'd say we earned every penny and launched a really successful product really quickly. Failures can happen too and they're usually a lot more complicated than just incompetent developers. It's just as likely the client is unable to articulate need accurately and corners get cut.