Ethics committees are there to protect both the institution and the subjects of the study. One of those protections is avoiding misleading the subjects, unless absolutely necessary and beneficial. How many times have you seen people here on HN bitch about Company X's misleading marketing? It's exactly the same with human studies - people feel used and abused when they find out they were lied to. Similarly, jancsika below points out that the author is working on a patient population with literal paranoid people in it; they're not likely to respond well if they find out a questionnaire was for a different purpose than stated.

Sticking to a common set of rules and only deviating when there's very good reason is one way to help protect subjects. What's the 'outcome' here? A doctor wants to do a study. Why is that more important than the rights of the subjects? Yes, everyone who does a study thinks it's going to cure cancer and solve the national debt. They'll promise the moon in order to get their way. These processes are put in place to protect people against poorly-planned studies. And there's no way to know ahead of time that a study is 'trivial' - if you're working on humans, you need to be vetted. "But we already do this to patients anyway" is besides the point; if you let doctors bypass vetting because of that argument, you'd see all sorts of horrific stuff happening. Ethics committees didn't come about because bureaucracy invented them for the sake of it, they came about because people were being unknowingly tested on by medicos who promised that the study was 'beneficial for the common good'.

And what you find distressing is not what other people find distressing. Search for mncharity's comment elsewhere on this page, where people are distressed simply by being asked about viruses. Yeah, sure, that's not typical, but the counterpoint is: is the research beneficial enough to warrant causing distress to people who would otherwise have been left alone?

In short, this 'needless bureaucracy' is there to protect both the institutions and innocent people from researchers going 'rogue'.