Something like Talocan at Towers would be very marketable at a fraction of the cost of a coaster. Don't know what their beef is with flats.
High throughput coasters, dark rides, and transport rides can get through far higher volumes of people per hour than a series of flat rides, which often have long loading times and low throughputs per cycle (unless you invest in something particularly high throughput like mystery castle). That's why you see a very low amount of flat rides at Europa Park, and if there are flat rides they are mainly higher throughput ones like a swinging ship or an observation tower.
In the case of towers though, they've removed most of their flats and not replaced them, so the capacity of the park has been reduced considerably given they've removed a handful of rides and there's now less attractions to experience. Had they been replaced with people-munchers, like dark rides/coasters/scenic high throughput track rides etc, then this would be more understandable.
At the end of the day a lot of flat rides don't age well and are hard and expensive to maintain, and often cheaper to sell off than repair. Your example of talocan is actually pretty much the opposite to the reality, it's made by one of the most unreliable manufacturers, Huss, costs a lot of money, time and effort to repair and will reach the end of it's life cycle far quicker than a more permanent investment.
Just look at talocan. Last year it had so many issues. They had to provide the carriage with brand new restraints, replace the brake and then the control panel. It then ran ok over the second half of wintertraum only to completely break down again at the beginning of this season. Over lockdown the whole gondola had to be shipped away for maintenance yet this didn't even help. The ride is now stuck on the worst cycle I have ever seen talocan perform...
I fear for the end of it's life, and it's one of my favourite rides. I am a flat ride person, but this shows why they might not be sustainable in the long run for parks. But in the case of towers, they've removed a handful of flats and a dark ride and just left the empty plots, which in my opinion is not desirable as it reduces the amount of things to do in the park.