Because then you have to maintain a publicly accessible server, and he has to maintain a database of everyone who has clicked the button. It wouldn't be "spammi

Because then you have to maintain a publicly accessible server, and he has to maintain a database of everyone who has clicked the button. It wouldn't be "spamming", just loading a tiny endpoint once a day (or less!) is a trivial amount of traffic. Doing it your way would be completely unworkable.