1. In terms of US monopoly status, the USA chart would be more relevant than worldwide (also tangential but is Baidu really that weak in China or is there just no data?)
2. Google certainly has a stranglehold on mobile search (unsurprising given that both Apple and Android use Google search). In USA desktops Bing still isn't that strong, but it is 10% and not very low single digits. It makes sense to me that search volume has moved to mobile. It's super convenient to search quick things on phones wherever you happen to be vs finding a computer. But if for example a remedy was to essentially ban Google from Apple's mobile devices then it would really move the chart quickly given Apple's dominance in US mobile marketshare.
3. The biggest issue is those are percentages and not volumes. If search becomes irrelevant because people switch to other modalities it's not going to appear as a decline in these charts.