So obviously the disk not spinning isn't the cause right?
Well, yes and no. It does come back up to speed after enough tries. Though as I mentioned above, it could be that the drive is spinning fine, but the read/write heads aren't working correctly.
Looking at the new iMacs I see they no longer have an optical disk drive. It's like what Apple did with floppies. But it also means you no longer get a system disk. I feel like I'm being corralled.
It's been like that since Lion, 10.7.x. Windows users have been going without included system disks on many makes longer than that. It's all about eliminating the cost of physical items you rarely need. It costs a lost to produce those things, and people routinely lose, or throw them away.
At any time, you can boot into Internet Recovery Mode and install the original OS the Mac came with on a bare drive. As long as you have an Internet connection, that is. What users normally do with newer Macs is to immediately make a clone of the main drive to another drive. Then you can always clone it back. No need for disks, or an Internet connection. The best solution is two separate OS partitions on an external drive. The first being a clone of the Mac the way it came so you can get back to the original configuration at any time. The second being a clone of your drive as it currently is. That one includes any OS upgrades, your third party software, etc. It again makes it pretty simple to restore your Mac to the last state you cloned the drive. There's also always Time Machine, but that's the slower method since you need to reinstall the OS from Apple's servers via the Internet, then merge in your TM data. A clone that's kept up to date is a much faster way to restore your Mac.
External optical drives are cheap. DVD drives in particular can be had for under $40 for a read/write drive. Blu-ray capable drives aren't all that expensive, either.