Why are trigger functions for entities and items not supported? And how do I use them in notepad?

When I go to create an entity or item, I want to add some triggers. That's the usual thing to do with entities and items. However, I see that 80% of Bedrock addon features in MCreator are not supported, including Triggers.

Why are they not supported? And how do I type this in code form if I want to add triggers, entity inventory, and particles?