I'm sure some of the hustle and bustle is due to the novelty, much like how WeWork was when it first launched in the US. However, you're right that there is a real lack of flexible month-to-month space in Japan so that may be a lasting advantage.
But anyway, maybe I haven't seen the cheaper Tokyo co-work spaces. If you have some convenient points, I would appreciate a pointer!
Edit: I'm actually in Shibuya every few months. When I'm there I work in the Shizutetsu bus station. If you see a middle aged white guy there programming, come say hi ;-)
I don't remember the specifics off the top of my head, but I'm sure there are/have been ~300 yen/h ones in for example Shibuya.
There's a smaller one called Open Source Cafe that lies a 5~10 min walk from Shimokitazawa station - that it's off makes it quiet and nice, and they host meetups from time to time.
The market rate for a fixed-desk designated membership seems to lie around 40,000 JPY / month in the hotter areas like Shibuya and Shinjuku, which is ~20$ per day if you only go there for weekdays. I think that's quite reasonable. I think WeWork has been part of driving this change, but it's definitely overpriced as things are now.
He was charmed - it worked on Benchmark as well but at least they didn't bet the farm in followon