The terminal is absolutely full of apps though. It's literally an environment designed around invoking other programs.
Pipelines are indeed very powerful, but mostly for a specific class of tasks. As soon as you need interactivity, the pipeline model losess a lot of benefits. None of the popular databases, web servers, games or office suites are implemented as terminal pipelines. The other problem with pipelines is that while they scale reasonably well with data size, they don't scale quite as nicely with task complexity. A five-program pipeline with complex command line arguments can already be complex to understand. A 500-program pipeline would be a total nightmare, especially when it starts including components for error reporting and retry behavior.
Pipelines are indeed very powerful, but mostly for a specific class of tasks. As soon as you need interactivity, the pipeline model losess a lot of benefits. None of the popular databases, web servers, games or office suites are implemented as terminal pipelines. The other problem with pipelines is that while they scale reasonably well with data size, they don't scale quite as nicely with task complexity. A five-program pipeline with complex command line arguments can already be complex to understand. A 500-program pipeline would be a total nightmare, especially when it starts including components for error reporting and retry behavior.