Adding to this, but I’m also not aware of many great Product Managers, UX designers or UX writers contributing to FOSS. Many devs have worked with shitty PM’s and like to dismiss their value, but a great one can make a massive difference in the quality of a product.

Same with the extensive UX design and UX testing that goes into making great products.

Believe it or not but I’ve seen the mobile apps be required to use totally different abstraction layers than websites, usually due to different authentication and access management methods.

“Back-end” is often relative when talking about these old systems. There are sometimes multiple layers of abstraction with different business logic built into each layer.

It’s fixable of course, but it is costly to unwind 30-40 years of bad technical decisions made by business people who never understood the systems they were making decisions for.

I might know the answer to your last point. I have experience working with financial services and large old institutions.

In short the front end is likely lighting fast and lightweight but the services it relies are incredibly old and outdated. Like mainframes running COBOL old. There is likely some abstraction but there are also likely literal decades of technical debt. Sometimes a call to understand what should be simple like what accounts does this client have might need to call multiple legacy systems that were integrated over the course of multiple acquisitions.