Four of those six (I think only running this week as STP?) are all "runs as required" services rather than normal planned trains. I don't really see any reason to take passengers on an excursion through a diversionary route just for the sake of it, especially when they aren't in any way guaranteed to run.
5O10 (morning ECS) is also running as a variation this week only to take the route via West Croydon (WCY).
5V82 (night ECS) is booked to run via WCY regularly.
You could similarly ask "why does train X runs fast through station Y late at night?". I find myself asking that whenever I hear the
last Thameslink of the night run fast from Haywards Heath to Brighton, or see a Thameslink run
ECS from Brighton to Three Bridges when it could be helping out nightlife enjoyers who are residents near Brighton.
The answer is probably time, money and that ECS movements are less "guaranteed" than a passenger movement, and adding an additional late night service (especially last service of the day) could prove problematic for the operator and for passengers when it's suddenly removed for a possession or another reason.