Some of us with mac pros or hackintosh literally can't update to mojave, because of missing nvidia drivers. And high sierra was such a clusterfuck that I'm glad I missed out on it.
If you have downloaded it previously, it prompts you if you want to “download the last compatible version”. As long as you’ve downloaded it previously you can redownload it.
"Extended support ends in September 2019. iTunes, in August 2020" [1]
And while High Sierra (10.13) had its quirks [for which I could understand your response, plus all non Retina only work with 10.13 as latest, officially), Mojave (10.14) has been smooth. If not only for the dark mode (finally!).
We test with machines that have it, but we don't operate day to day on 10.14. It's more about offering backwards compatibility so the majority of users can benefit.