Never figured out why they don't just use single digit numbers for WiFi? Instead of a confusing almost identical set of digits and numbers that can confuse unless you know what is what (I'm not into knowing every detail) why can't they just say WiFi 4,5,6 etc? We use 3G, 4G and 5G and we pretty much get that at a glance.
Lets wait for the Geek in the room to say something different.
It's an IEEE standard. All IEEE standards are numbered. The 802 family is for local area network standards. IEEE 802.3 for example, encompasses ethernet standards. IEEE 802.16 is WiMAX. Bluetooth was originally IEEE 802.15.1, though subsequent versions have not been maintained as IEEE standards.
IEEE 802.11 just happens to be for WiFi.
There's no reason why consumer products can't use a different name than the IEEE standard name to describe itself. Apple, of course, uses the AirPort branding. They did the same thing with IEEE 1394a, calling it "FireWire 400" instead. Sony called it "i.LINK". Then there was IEEE 1394b, which Apple called FireWire 800. Oh and by the way, Apple calls their ethernet plugs "gigabit ethernet" but it's really just 1000BASE-T, as defined by the IEEE 802.3ab standard.
If I had to guess why 802.11<letters> has been used so much in the consumer space, is because not all the 802.11 standards are compatible with the same antennas, and many WiFi devices support multiple standards, so it's useful to know exactly what you're getting. Specificity is a good thing, so you don't accidentally buy two devices that can't talk to each other, or can't talk to each other at full speed. From a consumer perspective, it probably would have been a good thing if 802.11a had never existed. Maybe without it, we'd have gotten more consumer-friendly names like "WiFi 3.0". Of course, there's absolutely no reason why companies can't sell products using their own little names.
Oh, and don't let the "4G" fool you. There's a number of different cellular network standards that are called "4G" that are not at all compatible with one another nor operate at the same speeds. The same was true of "3G" before that, there were several competing standards.
If you want, you can probably think of 802.11ac as a fourth generation WiFi standard, though. Call a and b first generation, g second, n third. There's an 802.11ax in the pipeline that will be the fifth generation.