I know how I'd answer your question.
FreeBSD back then did not want to install on my PC. First problem was that I had an IDE CD-ROM and they only supported SCSI CD-ROM.
Second problem was that it would not install in the unpartitioned space on my DOS/Windows SCSI hard disk.
Linux supported IDE CD-ROM and could install on the same disk as DOS/Windows.
Result: I installed Linux, and have used Linux ever since then when I need a free Unix-like system.
According to their forums, there was no IDE support because nobody would seriously have IDE on a server. At the time you could make a reasonable case for that for hard disks, but not for CD-ROM (especially since IDE CD-ROMs were around $100 and SCSI CD-ROMs were around $400).
The disk sharing limit was because they didn't think you could reliable infer the cylinder/head/sector (CHS) to logical black address (LBA) mapping that the other operating system(s) on the disk used. (The standard PC partition map at the time specified everything using CHS addressing, but disk interfaced had moved on the LBA addressing. Someone had to make up a pretend geometry for the disk, and then everyone had to consistently use that mapping to convert between CHS and LBA).
In theory, you probably could find a legal partition setup with free space that was unsafe for another OS to use due to ambiguity of the mapping, but in practice that did not happen.
[1] https://en.wikipedia.org/wiki/UNIX_System_Laboratories,_Inc.....
Linux went beyond "could install on the same disk as DOS/Windows". Linux could install on the same filesystem as DOS/Windows. No need to repartition, no need for unpartitioned space. If you later decided Linux was not to your liking, you could simply erase your Linux directory.
Result: I installed Linux on my C: partition, choosing a distribution which came with UMSDOS support. Some time later, I noticed that I rarely booted into DOS/Windows anymore, so I moved everything from the D: partition to the C: partition, erased the D: partition, and reinstalled Linux on that free space (using ext2 instead of UMSDOS). I have used Linux ever since then.