In what sense do Bing and DDG not matter in search?
They have less market share, true, because Google has a better product. Your argument seems to be that Google doesn't bother to have a better product (in search), because Google has all the market share, because Google has a better product.
(a) Google has a better product (in search) to which they had no real competitor for 17+ years.
(b) it remains better than those non-competitors even though Google has decreased its quality over time (worse results and more ads and BS)
(c) whether it copies/embeds third party stuff or not plays little into it. Nobody would switch to Bing just for those , after comparing the respective search quality, which is still better for Google.
So my argument is:
Google doesn't bother improving its search results -- on the contrary it lets them somewhat decline over time too -- because it has all the market share and better results than the competition.
If you are 80 points (fictional unit for illustrative purposes) better than the competition, you can let it slip to 70 or even 40 points better, and people will still use you.
In social media (e.g. against FB, maybe), but what competition does Google have for search?
Neither Bing nor anything like DDG matter.