Think about it. Do you bring your pet to a new neighbor’s house without asking first if they’d pet sit in their own place? That’s too presumptuous. Okay, I know some people who would, but they are not well received. Therein lies the problem. You don’t want to alienate the reviewer out of the gate. No way! Will not bode well for your book.
Many reviewers explicitly state not to send them a copy of your book until they have accepted it for review. If you just send it to them when you first approach them, you are doing either one of two things.
First, you didn’t read their review policy at all. They put it out there for authors to read and use, and you just ignored it. The purpose of the review policy is to communicate to the authors and/or publishers how to go about asking for reviews and what books the reviewer will potentially accept. If they inform you not to send manuscripts without prior approval, to do so will pretty much void any chances of a review. Kind of defeats the purpose of asking for a review.
Secondly, it gives the appearance of your arrogance. You don’t care what they require. You’ll do whatever you want. Now, you might not really feel that way, but that will be what the reviewer sees. And that will not help your cause.
Read the review policy to see if the reviewer accepts the format(s) your book is available in. Then contact them, asking them if they would be interested in reviewing your book. Then you can send it if they accept it and are willing to read and post a review. Remember that you are approaching them on their terms. Be polite and humble in order to get a better chance of getting reviews.