As someone who has been in the PCB industry for the past decade, it has been fascinating to watch how quickly KiCad came out of nowhere and quickly gained adoption as soon as CERN started contributing. After spending years in the software development of capture/simulation/layout tools for PCBs, I have come to see that these tools are not easy to create and maintain. Most products in the market are the product of decades of work.

We added KiCad support for our libraries on SnapEDA about a year ago, and now it's the 4th most popular tool on there with about 10% using it (after Altium, Eagle, and OrCAD/Allegro). When we talk to KiCad users, many are startups. However, I recently spoke with an engineer at a major defense contractor who uses Mentor Expedition at work and KiCad outside of his job. This is a sophisticated engineer who has chosen KiCad over the many free options available in the market. I had the same experience with another engineer at a medical device company using Allegro at work, and KiCad on the side. KiCad may not be as fully featured as the others, but it's being chosen as the next best alternative to these high-cost tools.

I agree that the UX is very quirky but EDA tools in general (other than Altium) traditionally have quirky interfaces.