I have always wondered that.
For example, If I search for the term "composer" or "what is composer", it shows the php package manager. Why does it show programmer-related results? Obviously, it makes sense that it does that, since the results I get are much more relevant to me.
What if an aspiring composer googles that? What results will they get?
Another example is, if I enter the word "spring" to the search engine, it shows the spring framework, instead of, let's say, the season.
So, my question(s):
Yes. This is the very core of Google's business model. The same data that influences search results is also applied to ad placement (see their real-time bidding system); when you do searches, it's likely you will see ads about the same subjects fairly soon afterwards.
Incognito mode is a very limited form of anonymisation; it's really not very anonymous at all. If you visit a page in a browser that has some google-controlled element (e.g. Google Analytics, a CDN JS library, or a font), then shortly afterwards perform a google search, there will be very many points in common that allow google to match you as very likely the same person (e.g. your IP, time of day, recent similar requests, user agent string, window size, fonts available) even if it blocks cookies that would identify you explicitly. This form of fingerprinting is quite hard to avoid, though Safari is a lot better at it than Chrome. Tor provides much more robust anonymisation by normalising many fingerprintable elements, as well as hiding your IP.
That's difficult because making use of all this information will indeed lead to generally more relevant search results, so it's in Google's interests to use whatever it can (within technical and mostly legal limits). Tor will disconnect the search results from you, but it may instead provide you with results linked to whoever else might have been using the same Tor exit node as you recently, which might not be pleasant! The same would apply to using VPN services.