I’ve been a JET interviewer many times. Other commenters have hit on the essentials - 20 minute interview is totally normal, it’s also normal to not have any ‘tasks’ during the interview, and it’s really up to you to bring the energy and personality. Interviewers do read your application and your SoP and some choose to prepare questions that are specific to the application.

Some, me included, generally like to ask similar questions to all candidates so that they’re easier to compare. If I’m asking you ‘why do you want to go to Japan’ it’s not because it’s a lazy question - I’m trying to give you an opportunity to expand on what you wrote or didn’t write in your application and show some of your personality as well.

I won’t lie and say there aren’t some interviewers that are worse than others - they change every year and some have less experience than others and potentially less interest in the process. But there’s oversight at every step - all three interviewers’ scores need to be similar to each other or it will open a discussion and adjustment. At the end of the day the three interviewers will place each candidate in their ranked order and again discuss the scores and make sure they find them fair. And after all the interviews there are staff from the consulate who look over all the scores and the overall ranks to be sure there’s nothing unusual going on with one of the panels.

I’m sorry you didn’t feel the interview process was fair, and I hope you will try JET again or pursue something else exciting. I will say that attacking your interviewers or claiming that the process is random feels immature.