A bait and switch would imply more of an implicit contract than there ever was along the way.
In the 90s, people were making websites because they wanted to make websites, and some of them were informational, and some of them were just whatever cool thing somebody decided to publish. Keeping track of your favorite sites was harder, but eventually browsers added bookmarks and it became a bit easier.
Okay, now how do you find all of that stuff? Three answers kind of sprung up: sites that are list of sites, directories (Yahoo) and search engines. They kind of work, but finding good stuff is still hard, and while the best answer here is probably search, the indexes aren’t entirely comprehensive and the algorithms aren’t good at sorting good stuff from bad stuff yet, they’re too easily gamed.
Google came along and went with search, but they did two things differently: they built a comprehensive index and they had a good algorithm for sorting good stuff from bad stuff. This didn’t stop an entire industry from springing up to try and game it, but they made gaming their algorithm an increasingly expensive proposition, and just doing the right thing easier.
So now we have a good search engine with a comprehensive index, now the web has a different problem: as much stuff as there is, it turns out there’s not enough stuff about a lot of stuff, and this is obvious once you have a good enough search engine that will till you whether there is enough stuff about your term. Well as it turns out, it is already 2004 and people are just now figuring out how to make lots and lots of money with this internet and web stuff. Google has come out ahead of the pact as the obviously superior choice for searching all this stuff, their competitors get a lot better, but Google stays ahead of them, and they’re able to maintain a lead by simply being so much better there is no reason to stop using Google so long as they’re not evil.
They also figured something else out: people are looking for information, or the tools for getting that information. Who knows more about getting information than peoples whose jobs it is to find and surface the right information? And it turns out that some things you can’t find with just a webpage, you need other kinds of tools, like calculators. So they built them in, because at the end of the day, it’s the information that people actually want, they don’t need the debris that comes along with loading a full webpage.
tl;dr Google is an information services company and always has been. Characterizing them as a search engine or advertising company is a massive understatement and was always inaccurate.