There may be two main reasons why partitioning isn't a well supported feature on optical media:
- Optical media was at the beginning small (in comparison with HDD's).
- Optical media was read-only. This later evolved due to easier access to consumer-level disk burners and the advent of RW technology.
Nowadays, there are much better solutions such as pen drives or even portable HDD. Not everyone has a Blu-Ray reader and not everyone wants to purchase a RW DVD. As such, in what regards optical media, partitioning was never demanded enough for it to happen.
I do have to point out the answer Rod Smith gave to a similar question, which I'm now quoting:
There are exceptions to this rule, though. Some Mac discs are written with a partition table and HFS or HFS+ instead of or in addition to ISO-9660. Such discs use the Apple Partition Map (APM) partition table. Some Linux distributions' installer discs use ISO-9660 that coexists with a partition table, but the intent here is to support different media in differnt ways -- when the image is burned to a CD-R or DVD, it appears to be a partitionless ISO-9660 disc; but when it's written to a USB flash drive, it appears to be a partitioned hard disk. This trickery works because of gaps in various data structures and the different sector sizes used on optical media (2048 bytes) vs. hard disks and USB flash drives (512 bytes). Both of these examples (Mac discs and Linux installation discs) are hackish extensions to the standards of ISO-9660, MBR partitions, and so on.
As you can see, it isn't technically impossible to do, but where it's done it's to provide additional support that couldn't be done in another way.