Getting UX right is a lot harder than people realize for several reasons:

- You have the usual BigCo problems in software with prioritization and incentives and pressure to deliver new features

- Front-end work is less mathematically complex and is generally undervalued by large companies that rely on complexity as a metric for difficulty/value

- When you use a piece of software all day for months/years, you learn the happy path to get things done and you forget all the rough edges because "it works fine for me"

- It requires a lot of detailed thinking about how other people perceive your work which is not something that software developers tend to excel at

- The user story which led to the UI/UX is not explicit to the user and the ways that users will try to use your UI are almost infinite

- Writing tests for front-end code has historically been more difficult

- There are a large variety of devices out there and testing on them all is time-consuming and painful

- Software is hard. People are hard. Combining them is harder.

- Small companies have a small surface area (people x devices x products) to cover and thus get more focused attention from their devs. Large companies have team reorgs and turnovers and many people who might have different priorities working on the same product

- Large companies know that people will still use their products even if the UX is worse because breaking out of the Apple/Google/Microsoft ecosystem requires significant tradeoffs

- Bug reports from the general public are given lower weight at big companies because of scale. When you have 10 bug reports to sort through it's not that hard to prioritize and ignore, not to mention that early adopters and small software users are more likely to be good bug reporters. When you have 10,000 bugs of which 9,000 of them are filed by people who don't know how to explain the problem: "my X doesn't Y", you become numb to new bugs unless they are show-stoppers, which many UX bugs are not.