There are a few reasons. Some of them are in the users’ interest. Lots of people phrase their search like a question. “How do I turn off the wifi on my blue windows 11 laptop?”

While ignoring stopwords like “the” and “a” has been common for a while there is lots of info here that the user probably doesn’t actually care about. “my” is probably not helping the search, “how” may not either. Also in this case “blue” is almost certainly irrelevant. So by allowing near matches search engines can get good articles even if they don’t contain all of the words.

Secondly search engines often allow stemming and synonym matching. This isn’t really ignoring words but can give the appearance of doing so. For example maybe “windows” gets stemmed to “window” and “laptop” is allowed to match with “notebook”. You may get an article that is talking about a window of opportunity and writing in notebooks and it seems like these words have been ignored. This is generally helpful also often the best result won’t have used the exact same words that you did in the query.

Of course then there are the more negative reasons.

1. Someone decided that you can’t buy anything if your product search returns no results. So they decided that they will show the “closest matches” even if nothing is anywhere close. This is infuriating and I have stopped using many sites because of it.
2. If you need to make more searches or view more pages you also see more ads.