Ok, after asking asking several people about this, it turns out that this change has been live for two weeks.
The reason behind reducing the default limit was to hinder bots and to reduce server load (bots were running large scripts which, in return, caused lag). Three actions per tick was chosen as, from data, that was the maximum number of actions that the majority of the playerbase could feasibly manage without extra "help".
Our engine team are currently considering whether to increase the number.