Because, obviously an EOL kernel is not getting updates and fixes anymore, it is by definition not supported (not sure where you get the idea that an EOL kernel is still “supported”, maybe you need to share your definition of “supported”), but yeah, by definition, an EOL kernel is not supported, as it is End Of Life, it is in the name. So basically, when you report issues, you don’t report them by testing on EOL kernel, it is common practices. You use the current and recommended kernels.