How hard could it be to implement a hard "include only these words, exactly as I spelled them"?
The issue is, I think, that those of us who want search engines to work exactly like that are in the minority.
Tiny, tiny minority. And if you think you want that, you're wrong!
Also, it's worth pointing out that finding matching pages in a database of pages is indeed trivial -- and building that is utterly insufficient, because for any query that trivial matching algorithm will return a huge number of pages. Thousands, even for the most obscure technical terms, millions or tens of millions for more-common words.
The hard part of building a web search engine (and it's very, very hard) is ranking the results once you've found them, so the thing the user wants is on top. That was, in fact, Google's big innovation: PageRank was Larry Page's idea for how to rank pages by examining the link structure of the web and prioritizing pages with more inbound links. That specific mechanism quickly broke down when SEO companies began exploiting its structure, but in addition to being gameable, PageRank had another problem: What if the search terms are used in multiple domains? The classic example is the query "python spacing". Am I looking for information about how large an enclosure I need for a captive python, or am I asking about indentation in programming?
So Google, and every other competent search engine, has shifted towards supporting queries in natural language, as well as using contextual information when available, such as the user's search history -- in the "python spacing" example, unless the user is a zookeeper who also writes code, their search history will point to the correct domain.
If you're writing queries as lists of terms that you want matched in pages you're doing it wrong. You'd actually be unhappy with a search engine that gave you exactly that, and you're also artificially reducing the effectiveness of the much better search engine you're using. Try typing questions instead, e.g. "How much space does a 10 foot Python need?" (correct spelling, capitalization and punctuation are not really required, but I use them anyway). This will give the engine more contextual clues about what kind of thing you're actually looking for and you'll get better results.
That said, it should be pointed out that if what you really, really want is "include only these words, exactly as I spelled them", Google will give you that. Just put them in quotation marks.