I don't know much about filesystems, but why haven't these been ported over to Windows/Mac and other OSes?
because MS and Apple are monopolistic and oppose open source technologies.
If MS added support to an open FS then nobody will use MS's own FS anymore. making the open FS the defacto cross platform standard. And by being cross platform it would be easier to migrate away from MS.
Because there is no widely compatible alternative.
NTFS and HFS+ are MS and Apple proprietary. Ext2, 3 and 4 are Linux only.
exFAT is MS proprietary and restrictively patented, so has limited OS support.
While FAT32 is a MS proprietary file it is openly licensed, so has universal OS support.
One more thing of note, journaling filesystems are not good for thumb drives (SSDs) without wear leveling (pretty much any USB stick does not have wear leveling while every full sized SSD does).
As such FAT, FAT16, FAT32, and exFAT are the only suitable MS FS for a thumbdrive. exFAT was made explicitly for such drives (you are better off with NTFS on a mechanical drive or an SSD with wear leveling).
ext2+ are all journaling file system, so stick to FAT32