There are plenty of trips where the ring road is the most direct route, or at least a lot more direct than the side roads. People don’t only use the M25 to go all the way around London after all, especially if they live close to one exit and have a destination just a few miles away along it.

There is absolutely reasons why a bike trail paralleling the road make sense, especially given that it is grade separated and even without that wouldn’t involve crossing near as many intersections as weaving around side roads just due to the number of streets that stop instead of crossing it. Given how incomplete the bike lane network is on the outskirts of London, it’s liable to involve a lot of biking on the road anyway, though the speed difference of a motor way versus what the bike can do does make it rather extreme.

Motorbikes travel the M25 all the time, they are just capable of speed’s sufficient to keep up with traffic, which makes half the article being police’s complaining about the bike being unsafe because of it’s slightly higher top speed even more silly, as in this case it was only unsafe because it was so slow.