> And then, a follow-up: what is actually the bottleneck at most companies? What causes "requirements gathering" to take long?

Complexity.

In my experience (medium size businesses, i.e. 200 million to 2 billion annual revenue) we're trying to understand how a complex set of systems and business processes and different businesses (external partners) interact and then trying to morph all of that into a shape that now has capability X layered on top or in the middle.

Here's a concrete example, business X that makes their own products and has retail stores as well as an ecom site wanted to add the ability to put complementary items built by other companies on the website and have them drop shipped from the vendors to the consumers. The final solution involved 21 different interfaces between 4 different systems (ecom system, store system, omni channel system, external drop ship mgmt system) as well as a new internal system to manage this activity. It's takes a significant amount of time to understand and solve for all of the low level details.

Isn't the answer to both questions straightforward? Real life is complex and has nearly infinite degrees of freedom. This means it's hard to approximate in software. Over time, real life, your understanding of it and your approximation (the software) all change. Keeping the approximation accurate enough that it's useful takes considerable effort since now you need to understand both the real life and the previously existing approximation of it.

What do they do ? Give power to their management ? "I am responsible for 50 people, I am important". "I managed over 250, I am important, give me money".