I imagine the following combination of factors.

1. Most people were not educated about it, had no clue it existed, let alone how useful it can be. Very few users truly used it (acording to what another search engine told me).

2. As a corolary of number 1, they felt they could pinch some pennies by removing that function.

3. When they did, also as a corolary of number 1, they noticed that the outrage was not in sufficient volume to be a threat.

4. Apple removed the ratings system on the apple store, in order to be able to sell the possibility for rankings to be sold instead of deriving from user satisfaction.

5. Most people being casuals did not even notice that it was gone. No public outrage.

6. Corolary of 5 - Google app store followed suit, then Youtube did too, so did Tripadvisor, Imdb (for a while). And little by little, the possibility to filter content according to user preference started to fade. And content started to be prioritised according to commercial guidelines and not number of visitors or external links, perceived respectability, density of content and keyword relevance (which remain a parameter of the algorithm, but at a much lower rung in the ladder than before). Well, on keyword relevance, it's technically gone now that there's no exact search.

7. Google saw this and applied this commercial outlook to the search engine, not just the app store. They profited immensely.

8. Nowadays, the shape of the internet changed from a planet to the tip of an iceberg; but many new users weren't born before these changes, many more did not use those functions and even less of them would care.

I imagine.