My question is why cart_updated event is not showing in Contact’s History list?
It does fire, it’s exists in the Automations → logs.
if I rename it to cart_updated_2 or anything, then it shows up in the Contact’s activity list.
It is intended behavior to not show up if it’s name is cart_updated?
cart_updated is a pretty frequent event (fired every time something in the website visitor’s cart is changed - product, quantity, coupon) so it creates lots of noise that’s not necessarily meaningful in the history of the contact’s behaviour. It’s of course exposed to automation so that you can do cart abandonment or other similar automations, but it’s not shown on the timeline in order to keep the events on the contact’s timeline more meaningful.
Indeed you can find those events in the event logs for debugging purposes.
It’ll be great if you can let us know what might be the reasoning of having this event in the contact timeline - we can always revisit the topic.