It might seem like a shady practice, especially because it was set to function by default, but there's also a good rationale for allowing Google to do this, as it improves the sharing functionality across your Google accounts, and makes things like phone recovery much easier, in the event that you lose your phone and want to restore a new phone to the old one's settings. There's also a slew of quality-of-life features, from faster sign-ins to emergency location services, that work better or faster with this feature enabled.
Of course, there's also an incentive for Google as well, since connecting all your Google accounts via phone number helps to optimize their ad performance, allowing them to show you more targeted advertisements across your devices or accounts.
It is not about loosing your phone it is only about selling you!