Your publisher will not have guaranteed to you that search results on any given platform would bring up your book for any given phrase or subject. The reason for this is that it is mostly outside of the publisher’s control.
Search engine optimisation is something you may be familiar with for business marketing. If not, then please read this article on search engine optimisation at Wikipedia. Now imagine that whole search algorithm scenario but behind closed doors at each vendor (eg. Apple, Amazon, Kobo, Google Play). They each run proprietary software algorithms, which do many things to determine what books get shown to their customers. The ultimate aim is delivering the best quality, most popular, highest relevance results for searches on their stores.
Having optimised meta-data is important, but will not necessarily mean your book comes up for the kinds of searches you think readers who will want to buy it will be doing. A dedicated book marketing consultant is recommended to consider your unique situation, recommend keywords and other optimisation techniques, as well as help you marketing your book directly, to create a snowball effect.
One reason your book may not be coming up higher in search results on Amazon or Apple is because it lacks reviews and sales. These are both things that PublishMyBook.Online authors get trained on during book marketing consultations. Book marketing is a very specific art. Even if you are very experienced with marketing in general, book marketing is a deeper dive.