I published a novel in late november, and it's sales are low but steady to slowly increasing. A key aspect is that to "survive" past the initial bump you need to invest effort into building word of mouth and getting reviews, and that is a slow process. The people I got to help with marketing even actively advised against doing much marketing before we had a base of reviews, because they apparently find it almost impossible to get positive ROI on Amazon ads until there's a reasonable number of reviews.
I intentionally started writing a series, and everything I've seen and heard suggests series rarely even start selling decently until at least the 3rd volume, because people hold off to see if it's worth investing time in.
I'd advise against considering what happens to "most" books, because most books gets no marketing, no proper cover design, no effort in writing blurbs, no effort to push the books over time.