> IBM zSeries runs Linux in big-endian mode and is still a mainstream product.
For most hobbyist open source software developers, it's a niche product in practice. I can easily test on 32-bit and 64-bit x86 (most desktops and laptops can run it natively); I can easily test on 32-bit and 64-bit ARM (a Raspberry Pi 3B or newer is a common enough device, and using Termux on a phone is also an option); but how would one get access to an IBM zSeries?
> If your code doesn’t work on big-endian, it’s usually poorly designed.
The parent comment mentioned "subtle bugs". It's not hard to accidentally introduce byte order dependencies; one simple example (though from the big endian side) would be forgetting to use "htons" on a port number. Since more and more protocols and file formats are natively little endian nowadays, it's easy to miss a conversion between "little endian" and "native endian", since it will still work perfectly on little endian architectures.