Boarding the train at the last minute also unfairly disadvantages anyone who has made the effort to be there in good time. Late arrivals are often very adept at getting to the doors first.
Also at some places inevitable if the stock is not physically there yet. Lots of suburban services do have marginal turnaround times and a little bit of late running can make the timings for boarding rather smalll. One option is to just board the train prior to it physically being there once a train is confirmed being routed in; however platforms can get very congested (especially as arrivals try to get off too) and some operators are wary of that. However at some stations services are boarded before the arrival is there and it just about works, so there’s no hard and fast rule.
And I'm still waiting for an explanation of why e.g. the Swiss (and in fact most of europe I think) can include dispatch time as part of the travel time when the UK can't? (I know which system is more logical and easy to understand as a passenger...)
I did give you an explanation earlier but you seemed to not want to accept it. As I said before, xx:xx:00 departure time here means “train moving”. Therefore to actual get that to happen, the process will start 30-60 seconds beforehand. The solution to this is do a “public offset” to the timetable for all trains by say, a minute. I don’t know what the Swiss do, but it’s probably similar or the dispatch process is for some other reason much quicker. Ultimately though we’re arguing about very fine margins; just turn up for your train at a decent time. If a train is boarded late, it more than likely means it’s going out late.