I think one of the issues is that, if Amstel Gold is anything to go by, Dutch restrictions at present make closed circuit racing a more attractive option for lockdowns etc. in keeping racing going, and as such a motor racing circuit works from a 'you scratch my back, I scratch yours' kind of perspective - probably cheaper in terms of the hiring cost - especially at this time of year when few racing series are on - than the cost of policing and security of an open road course and helps both the bike race run and the circuit stay afloat.I wonder if the Mens Elite would allow such a poor stage. They had a similar one in the Womens Tour of Britain a couple of years ago. Around a sports track in Milton Keynes I think. Absolute dour.
I wonder if Barnes went for the lunge she would have taken that stage today? I only glimpsed at it. Great though from D'Hoore, great rider.
However obviously cycling has a long and storied history using motor racing circuits, but the long and complex, topographically interesting motor racing circuits of the past are mostly gone, only really the Nürburgring survives. There are some short circuits (more 'normal' length for modern day racing) which could be used - Brands Hatch, Portimão, Mugello, Spa-Francorchamps, Road America - and some like Bathurst-Mount Panorama that are kind of public roads but also used to being closed frequently for racing, but largely when we get more interesting courses at motor racing venues we're seeing stages either just arrive at the motor racing circuit (like the Laguna Seca stage in the Tour of California) or circuits which incorporate the motor racing circuit alongside some public roads (both the old Imola circuit resurrected in the Giro and the new one used for the 2020 Worlds). Unfortunately, most racing circuits nowadays are far too short to produce a particularly interesting cycling stage, and are far too flat to be selective, so we get a pretty dull spectacle as obviously you can't even go to the helicam for some tourist shots (I know there wasn't a helicam on today's coverage, but even if there was).
There's definitely a tendency toward the women getting a calendar with a lot more of this kind of tedious circuit race than the men, and the stage you mention - the Kent Cyclopark stage in the 2019 Women's Tour - was indeed pretty ridiculous, the stage lasted barely over an hour and the circuit was far narrower and shorter than today's too; the highlights show was essentially an hour long infomercial for the Cyclopark with added bike racing coverage.
It's worth noting though that the HAT is not a WWT event, and while the WWT has probably too much of those pseudo-crits (RideLondon and the Champs Elysées version of La Course particularly egregious examples, but the Tour of California had a crit in several years, the Madrid Challenge always has the tri-star Vuelta closing circuit (will be interesting to see what they do this year) and the Tour of Britain has had the CycloPark stage and the 2017 London circuit race), such stages do exist in smaller men's races too, just usually buried away in the pre-season somewhere. I'll not count things like the Izu stage of the Tour of Japan and the Krylatskoye Ring stages in the Five Rings of Moscow, on the basis that a) these circuits were designed specifically for cycling, b) these circuits are 12-15km in length and have a lot of up and down in them because they were designed to be selective, so aren't really what we're talking about here.
The 2017 Tour of Abu Dhabi included a stage on the Yas Marina Circuit, which is one of the worst motor racing circuits in existence and topographically even less interesting than Assen; the Vuelta a San Juan includes a stage on the San Juan Villicum motor racing circuit, and pan flat circuit races and crits crop up a lot in the Asia Tour. At the WT level, other than obviously the Champs and the Paseo del Prado, there's not many (as a side note, it bugs me when races that are only about five days long want to have a parade stage because they're aping the Champs Elysées). The Tour Down Under included a final day crit in Adelaide for many years, and when it existed the Tour of Beijing would always finish with a pan-flat stage and a short circuit around the Bird's Nest Stadium, but those are kind of out of the way of the main World Tour calendar. I guess maybe we could count the days when Tirreno-Adriatico finished on a road stage on the same out and back circuit in San Benedetto del Tronto they now do the 10km ITT on? Even then, Garzelli won the GC off Scarponi in 2010 by stealing intermediate bonus seconds on that stage.