Earthing/grounding started gaining traction among some of my friends and family at least a decade ago. It's a simple principle and there is some data out there to suggest it can have a positive effect on health. Until recently humans didn't wear shoes all of the time. I recall how in summer my sibling and I were mostly barefoot, except for when we needed flip flops to not burn our feet. We'd outgrown the previous year's school shoes and our parents weren't going to buy new shoes until the week before school started again.
For me, the whole earthing/grounding thing falls under interesting, because connecting with the earth's magnetic field and soil's rich microbiome via our bare feet is something humans have done most of our history. It doesn't hurt to spend more time in direct contact with the earth, and according to an article in the Journal of Environmental and Public Health, has been shown to improve sleep and reduce pain.
I tried earthing back in the early 2010s, but there was so much else going wrong with my health that it was like the proverbial bailing out of a sinking boat with a thimble. I don't think earthing is a magic cure for anything. But I do include it now in the natural health behaviors I use to improve my overall health (these include sunbathing, walking daily and preferably more than once a day, making sure I don't sit for 8+ hours a day, drinking enough water, spending time in nature at least weekly, spending some time barefoot to strengthen my feet, reducing stress, finding things that make me laugh, etc.).
I think the reason this may seem new is because someone figured out how to make a buck with it by selling grounding mats. You can earth/ground on unsealed concrete, so most people have options even if they don't have a lot of dirt and grass to stand on. There's no way I would buy a grounding mat, just like I didn't buy into the magnetic mattress hype.