I prefer it if authors don't send me hassling emails about why I haven't reviewed their book yet. The usual answer is simply that I haven't read it yet. I'm a slow reader and make it clear that I offer no guarantees about timing. At best, that's all you'll get told. At worst, you run the risk of sounding like an author who'll cause problems after the review goes live, which might make me change my mind about reviewing it.
This year, I didn't read much at all, because I couldn't cope with the heat (I basically spent the days lying on the cold tiles and surviving). It's not like I'm happy about not getting anything done for most of the year.
But on the original subject, most ARCs that I request come from NetGalley with a few from Edelweiss (I don't like that site as much, but some publishers only use it, so sign up for both). I've sometimes contacted small publishers directly. Most ARCs I'm offered are via email, though big publishers usually want to send the ARC by autoapproving it on NetGalley or Edelweiss.
Publishers are pretty open to new reviewers, but you do need the minimum of a blog where you've posted some reviews. If you don't want to review, don't ask for ARCs.