I like Collins point with one correction: "The main point I think is that
handlebars are kinda like saddles."
As a person who loves drop bars but has always hated how narrow they are, I love the recent developments. I own the Crust Towelrack (v2 - Full size at 670 mm) and the Crust x Nitto Shaka bar (520 mm). Wide drop bars are great for really maximizing different hand positions (so many!) This is my main reason for liking them. I heartily disagree with anyone who questions their ergonomics, even a little. The Nitto Mustache is 515 mm, the Rivendell Albastache is 555 mm, and the Riv Billie 580 mm, and the Bullmoose 670 mm! And modern MTB bars are even larger. No one complains about those being based upon "ergonomics that haven't been tested properly."
Personally, I have never liked alt-bars (Albatross, Bullmoose, etc), though I love the look of them. But that is me! If you want a wide bar and like not having drops, get some alts. If you want a narrow bar and drops you're all set. And now, if you've been jonesing for a wide bar with drops, you're time has come! I don't think there is much mystery to it. Yes you can fit a larger bag, but too me that shouldn't be a reason to get handlebars (though it is a nice benefit to wide bars). I'm also middling about the off-road aspect. I've never felt like 440 mm noddles provided too little leverage for a bumpy trail, but maybe I'm not shredding the gnar hard enough??
A couple of final thoughts: I think the Shaka bar strikes pretty much the prefect balance for me, so much so I bought another pair just the other day when Crust came back online. The Towelrack, although still really really good, have a few drawbacks to me compared to the Shaka:
Aerodynamics - yeah, yeah, I'm not overly concerns with Aero or anything, but you do pay a bit of penalty here, coasting down a descent in which your buddies speed past you without pedaling is just something that is going to happen compared to normal drops, even the Shakas (which I don't notice this with). Now compared to Alts, it's probably better, so if your decision is between the two, it's maybe a no-brainer, but something to consider otherwise (Basically I don't want to put them on a pure road bike)
Clearance - They are wide; be prepared to have to think a lot more about navigating some situations. On the open road this isn't a problem, but tight singletrack or urban bike infrastructure can suddenly become a bit more challenging. I think this may be more of challenge with wide drops compared to alt or MTB bars due to your hands being a bit more exposed due to the positioning, even though they are just as wide. Or, i dunno, maybe my bike handling skills are junk and I got away with narrow bars? Again I don't have this issue with the Shakas as much
Different pressure points - Not really a big deal, but do be prepared to get callous in different spots. I notice that using Towelrack tends to give me callouses inbetween my thumb and forefinger, whereas with normal drops I get them more on the base forefinger and middle finger.
In short, handlebars are very much a personal preference and wide dropbars aren't any different; they are not a panacea but I also don't think they are just a "trend." They are probably best for folks you like a lot of width for different hand positions and also want to maximum their reach on their bike compared to alt bars.