The fact that most people use the default, and that Google mandates the browser be Chrome and the search be Google for all Chrome web browsers (largest desktop market share) and Android devices (largest mobile market share). And that they then prioritize their own products and services in Search as well.
The issue isn't "everyone is forced to use Google Search" as much as "Google creates a monopoly through connected use of it's various products and services".
The issue isn't "everyone is forced to use Google Search" as much as "Google creates a monopoly through connected use of it's various products and services".