Reasons to read a book
Serious question: with millions of books out there, why should anyone read YOURS?
The higher price you charge, the more work your cover, blurb and reviews will have to do.
It's easier to give away books, to overcome most objections and balance out a weak cover or blurb, or lack of reviews. But just because something is free doesn't mean people are going to want it.
You still need to convince them to get your free offer in front of them, and you still need to convince them to buy it (a lot of authors try a free book giveaway when they launch, before they have any reviews, which is a mistake - and then complain that it didn't work, because they only got a few hundred downloads).
Assume half the people who download your book aren't going to read it anyway, and only 10% or so will enjoy it enough to take action (buying a sequel or signing up to your newsletter).
Also, however, assume the majority of free book offers aren't very good - because most authors don't want to give away their best stuff. Readers expect free books to be mediocre. You need to surprise them by being the best free book they've ever downloaded. You need to win them over.
You may also, however, need to encourage them to start reading the book even after they've downloaded it or are on your list (for example, an optin offer at the back of your Amazon book could be for a big giveaway prize, rather than a free book; then after they sign up but don't win the big prize, you can offer the free book as a consolation prize to everyone, with an extra giveaway for an easy quiz to get them to start reading.)