The challenge agencies have to deal with, that internal dev teams don't, is that with a contract software engagement, every conversation between the developers and the customers risks impacting the contract terms.

In an internal software project, when an engineer looks at a problem and realizes it can be trivially solved with an off-the-shelf airtable template, that's a win for everyone! Less code to maintain, less distractions from other more valuable projects, and value delivered sooner.

If a developer working for an agency realizes that, and says it out loud during a meeting with the client, they just undermined the basis for the entire engagement.