For many corporate client system developments this is my experience too. Producing the actual LOCs is not the primary cost; it's requirement gathering, figuring out how to plug in the new component into an existing system etc. As an example of the first, you might be digitizing a cross-department workflow. Your job now basically becomes to interview stakeholders from each dept and have them commit to a single online workflow. An example of the second is you might want postgre for your backend, but the client might want a single stop db on whatever they're using today.
Then there are challenges around integrating with existing APIs, workflows etc.
Let's not forget feature creep. Sometimes the client might not be able to visualize the final UX in its entirety (often simply because multiple people are involved),and therefore, they might only begin realizing its impact as and when parts of the new system becomes available.
Essentially, you are not paid to build an isolated system, but to understand well and play nicely with the larger context - human and technological - within which your system must live.
Then there are challenges around integrating with existing APIs, workflows etc.
Let's not forget feature creep. Sometimes the client might not be able to visualize the final UX in its entirety (often simply because multiple people are involved),and therefore, they might only begin realizing its impact as and when parts of the new system becomes available.
Essentially, you are not paid to build an isolated system, but to understand well and play nicely with the larger context - human and technological - within which your system must live.