Before thinking about corruption or malice, I like to try to assume good faith. And I see a couple things:

1. Most people don't write.

2. The people who write are not always competent.

3. The people who write often have an agenda, too.

What's the consequence of that? Imagine what the politicians receive: tons of messages of people complaining, most of which are factually wrong. What to do then? How to know who is right? It's genuinely hard.

EDIT: please write here: https://european-union.europa.eu/contact-eu/write-us_en

Probably some combination of all three.