It's totally lost its meaning in the last few years.
My guess is that is how it seems to you because the last few years is how long you've been in the writing game.
The NYT list has always been curated, and always been possible to buy your way onto. The only difference is now you are looking at it as an author, and the veil of mystery has been lifted.
PLENTY of readers still place stock in it. You are more likely to get a Bookbub if you have it, and people are more likely to click on your ads if you mention it. I've read research that says hitting the NYT list can boost a first-time author's book sales by over 50%. I'm not sure how well that still holds up, but I'd hardly say that it's totally meaningless.
You're probably right about it not being a sound investment for most writers if you look at it strictly from ROI on one book. But I know some nonfiction authors who make most of their money from courses and speaking gigs that are thrilled to have those letters. It is a mark of legitimacy to the average reader, who knows nothing about what is involved behind the scenes.
Speaking from personal experience, when people find out I am a full-time writer, they usually don't take it very seriously. Even when I tell them I make more now than at my old job, they still think it is a hobby for some reason. But when I mention I've been on the USA Today bestseller list a half-dozen times, they immediately change their tune.
You know that list doesn't mean much. I know that list doesn't mean much. But to the VAST majority of readers out there, it means a lot.
Also, there are a bunch of people on these forums that think it means something. People are constantly organizing promotions around list runs. Many writers have hitting a list as one of their writing goals. People on this thread have mentioned it as a bucket list item. To dismiss those goals as meaningless isn't exactly the most encouraging thing in the world.