They're Lying (But not on Purpose)
The art style you are referring to is using what is called Hyper-normal Features. You will often see it in comics, anime, hentai, cartoons, advertising etc etc. Basically, the parts of the opposite sex that your brain is wired to detect (assuming you are straight) are pretty specific. Hips, breasts, behind, and body proportions (slim neck, slim wrists, slim waist etc etc). In animal studies they took a wood pecker where the female has white spots and a red patch. They made a fake female wood pecker with a wildly exaggerated red patch and more numerous white spots and placed it next to a female. In the majority of cases the male began courtship dances with the exaggerated fake instead of the actual real thing. This behavior was true even when the fake female woodpecker was reduced down to simply being a stick with brighter than average white spots and a big red spot. They had hacked the animal's brain by identifying the traits the male's brain was evolutionary programmed to detect as sexually attractive. In this case, it was not an actual live female, but simply a color pattern.
This works for humans as well (though to a lesser degree because the traits we are programmed to identify are a bit more complex). But long and short of it, artists tend to draw women with wildly exaggerated sexual features because deep down inside your instincts are not very capable of telling the difference between a drawing and a real female, and will automatically be drawn to the exaggerated characteristics. This means you spend more time focused on the artists work, and are more likely to seek out more of it. In large scale art this is intentionally done to exploit this human psychological trick. Fan Art tends to simply imitate the style of mass media. For a literally 100% perfect example of utilizing hyper-normal features just google up Jessica rabbit from "Who framed Rodger Rabbit." (with safe search on preferably.) That particular character has been exaggerated to the point that her body could not even support its own weight or contain organs, yet she is one of the most common subjects of fan art projects, despite being a background character in a film from decades ago.
Wide Hips Are Detrimental to Mobility
Human infants are born in an incredibly undeveloped state, primarily because we have really big heads. This is why childbirth is such a painful and dangerous process for humans, because not only must the parent care for a totally helpless creature for a very long time, but even in the undeveloped state humans are born their heads are only JUSSSST small enough to pass through the human pelvis. One might be tempted to think "well, then why didn't we evolve wider hips and larger pelvic openings?"
Because a species whose females are not able to outrun predators, cover large distances, or catch prey doesn't survive. Due to our bipedal gait our hips cannot be too close together or too far apart, there is a sweet spot that maximizes mobility with a minimum detriment to surviving childbirth. Males pelvic structures are actually more efficient than females at running, load bearing, and long distance mobility, but males also don't have to pass a live infant through their pelvic opening either.
So, in summary, wider hips on a bipedal organism is great for childbirth, but terrible for mobility. Replace the incredibly efficient long stride of humans with a slow shuffling waddling pace and that's basically what furry/anime/fanart style hips would result in.
Flightless birds like the ostrich or emu are Digitigrade bipeds, however they have very narrow pelvic structures. Digitigrade bipedal body structure is highly effective at sprinting, but not a lot else. Unlike plantigrade bipeds, their knees and ankles cannot lock meaning that they must constantly be exerting much more effort when standing still than a plantigrade biped. They have sacrificed efficiency for speed, and thus have developed very narrow pelvic structures to take advantage of that. They also do not give live birth, which is another reason why their hips are able to be so narrow.