Sometimes compilers have bugs or are not fully-compliant. For example MSVC two or three versions ago didn't understand =delete. Standard library also might have

Sometimes compilers have bugs or are not fully-compliant. For example MSVC two or three versions ago didn't understand =delete. Standard library also might have errors. Moreover, we use third-part libs that are not always up to date (for various reasons), we have some legacy parts, and so on and so forth. I wish switching compiler required only setting another CXX. :)