Which trend line are you talking about? The only applicable one I see/remember is the figure labeled 'Marathon World Record' at the beginning of the article and that trend won't break 2 hours until around 2025.
People have to train and city road is not best of surfaces. So it is very possible that somewhere someone already ran faster than 2 hours, just did not care to record it or announce it.
I'm not a runner, but I know many. Training for a marathon involves running fast, and it involves running far, but typically not at the same time. I don't know anyone who runs a marathon distance in order to train for a marathon, you save it for race day because it takes a lot out of you.
The article also talks about drafting and the role of 'pace bunnies' in setting a record. For those reasons, I don't think someone has gone out on a 42.2k run and broken the 2 hour mark.
I follow competitive running closely; this just isn't something that would happen. Running a marathon takes a huge toll on the body. Professionals typically only run two a year (although certain East Africans sometimes do one or two more), and they usually take an extended break after each one. Competitive runners never approach race effort in their training, especially at marathon distance — it's counterproductive to do that sort of damage to your body.
There's also a financial incentive to run your fast marathon in a race, especially for the runners from poor East African countries who are the only ones capable of running close to the world record. The prize money is typically several hundred thousand dollars if you include the bonuses for breaking the course record and the world record, finishing faster than certain time thresholds, etc.
I find it pretty hard to believe that someone would maintain the level of fitness required to run a sub-2 hour marathon (a level which no recorded human has ever achieved despite devoting their lives to the sport) and not even track it.
