Because Google provides (or used to provide) a fast consistent interface for a lot of basic queries. Sure, if I'm researching etymology in depth then I'll go to

Because Google provides (or used to provide) a fast consistent interface for a lot of basic queries. Sure, if I'm researching etymology in depth then I'll go to a specialist site, but 90%+ of the time I'm just double checking the definition of a word or something like that. In general, internet browsing is biased towards sites that you're familiar with and can be reasonably sure aren't going to do something annoying (it used to be popup adverts and auto playing music, now days it's popups about newsletters / memberships or aggressive notifications about cookies / privacy notices.). This is particularly true if you ever spent time browsing in an open plan office or similar public place. There's also a cognitive load of interacting with a new interface which isn't something you want to deal with if you're midflow and want to check a word. This is not to say that those sites you mentioned are guilty of bad practices, but the point is I'm not a regular enough user of them to have them on my mental "generally trust" list.