The current version of npm does this and this is "correct behaviour". I got bitten by this a few weeks ago.
For the passers-by, the only way to make npm behave expectedly in this specific case is to use "npm ci" instead of "npm install". If you do not do this, npm will assume you want to update the packages to the latest version at all times, at all costs, even if you have a lock file in place, and even if you have your package file and lock file locked to exact versions. (i.e. 2.0.0 exact, not ^2.0.0)
This is a new addition, and it has been added a couple months ago. Before that, you had to check your dependencies into your source control. That might still be the best practice, and likely the only trustable way to get reproducible builds consistently over a longer time horizon.
Yes - to be more specific, you can lock your own package's dependencies to an exact version, but you cannot lock dependencies of your package's dependencies. You can't do anything about them. They will get updated because their package lock specifies the lock in the form of ^2.0.0. The fact that a package lock can resolve to multiple versions is counterintuitive. One would think the whole point of a package lock is to lock packages.
As a result, when you do a npm install in your oblivious and happy life, npm naturally assumes you want to summon Cthulhu. If you didn't want to summon Cthulhu, why did you call the command that summons Cthulhu? Yes, the default command summons Cthulhu because we believe in agile Cthulhu. If you don't want to summon Cthulhu, try this undocumented command with a misleading name we've added silently a few weeks ago for weird people like you who don't want to summon Cthulhu when they want to do a npm install. But seriously, why do you not want to summon Cthulhu?
Unfortunately, this was the impression I've gotten of the position of npm folks when I read a few threads about this. I've moved to npm ci for now and moved on. Npm's package lock is many things, however, none of the things it is, is a package lock.
For the passers-by, the only way to make npm behave expectedly in this specific case is to use "npm ci" instead of "npm install". If you do not do this, npm will assume you want to update the packages to the latest version at all times, at all costs, even if you have a lock file in place, and even if you have your package file and lock file locked to exact versions. (i.e. 2.0.0 exact, not ^2.0.0)
This is a new addition, and it has been added a couple months ago. Before that, you had to check your dependencies into your source control. That might still be the best practice, and likely the only trustable way to get reproducible builds consistently over a longer time horizon.