What ever happened to 24 mg. nicotine juice? Everything now seems to be 0,3,6, and maybe a 12 once in awhile. 6 years ago 24 mg. was everywhere. (Speaking in reference to the original, unsalted juices.)
I've vaped 24 mg juice from AVE since 2015. When I cut it down to 18 mg. there was a noticeable hit on the flavor. So now I'm hesitant about ordering any of these low nic. content juices and the salts are ok but not my go to.
The devices got more powerful, so most people switched to lower nicotine juices. Even today's MTL devices are a lot more powerful than the standard devices of six or more years ago. Also, I think DL is more common than MTL, so those devices vaporize even more juice and therefore require even less nicotine.
Higher nic juices have reappeared with the relatively recent addition of pod mods, but as you've noticed those users tend to use salts.
Where you are is also a factor, because a number of jurisdictions have limited nic concentration to 20 mg/ml.
Where you buy also matters. My goto juice source adds the nicotine themselves, so I can get almost any concentration I like.
For what it's worth, when I started dropping my nicotine concentration (24 mg/ml - 3 mg/ml, back when I was using a Protank and an Ego battery), I found the flavour got intolerably sweet and strong as the nicotine level dropped. I now buy commercially-made ejuice with twice the nicotine I want and dilute it 50/50 with VG and PG to get something that works for me.