I was bummed about it too at first but thinking about it more, having version numbers will make it more obvious if a device has outdated software to the normal consumer and might put pressure on manufacturers to update devices much faster
Sure, K comes before P in the alphabet, but figuring this (and the actual distance) out takes a lot more mental effort than comparing 4.4 with 9.
It also resolves the issue where you need to decide whether 7 is larger than Marshmallow - a question that would make people question your sanity if posed without context.
And to make it more confusing, each release had a separate codename used before the release, so you had Android K, Android Key Lime Pie, Android KitKat, Android 4.4, and API level 19, all meaning the same thing.
Now, if only we could get rid of the separate "API level" designator (or rather, turn it into an opaque enum, instead of using it everywhere)... because 28 should not be less than 10.
