> It doesn’t come across as genuine...

How can you determine if a thank you note is genuine or not if you don't read it in good faith?

One person might send a generic thank you that tells you nothing, and another might send a thoughtful message that in some specific way reiterates their interest and excitement in the job.

> ...and has no impact on anything...

Sure it does. I hired lots of people in my career and things like this helped me determine if the candidate was thoughtful, professional and interested. On multiple occasions, I hired people who didn't technically meet my ideal requirements but explained why they were interested in the role and gave me greater confidence that they were up for the challenge and worth taking a chance on.

Cynicism by default does not serve you well in any aspect of life.