In an ideal world, I'd agree with you: reinstallation of a particular program should fix everything. However, these registry optimizers sometimes fiddle around with the registry entries for system or common files that the program depends on; those files are still present on the machine--if the installer has the logic to install dependencies, it won't be invoked--and sometimes require particular registry data to function.
In the case of the "Password Manager", it's probably depending on a host of other components: fingerprint drivers, Client Security Solution files, Lenovo System framework files, etc. Vdery easy for things to be "brittle".
One of the dumb customer-unfriendly things that Lenovo has been doing in recent times is abandoning the creation of full-function installers (usually created with Installshield) that were designed to allow repair as well as uninstall operations using the Windows native installer database (there are other Windows installer creators that will do the same thing as well). Instead, most of their installers throw the files on the customers machines, register whatever the components need in the registry--and do the reverse when uninstalling
Designing such a repair facility is considerable extra work and expense for the developers, since every installed component has to be registered in the Windows installer database, and actions designed to upgrade, repair, or remove the different components of the installed program and their dependencies--which sometimes require changes to the design of the programs themselves to make that easier. But the upside for the Lenovo's customers is considerable: simply click on "repair", and return (with a bit of luck...) that program to the functioning state it was in when first installed.
And there is an upside for Lenovo as well: precisely documented effects and dependencies for each of their programs on the various Windows platforms they are installed on (i.e. configuration control), which is good for ongoing development efforts, and less customer frustration and long support calls.
.. I'm probably an older schmoe.
