It has been setup to save a big amount of memory on the server.
If we use C:\ProgramFiles\UiPath\Studio\Packages as package source, for all users packages will be stored at this path and no need of separate copies for each user which will consume at least around 5 GB storage space over the time.
If we use C:\Users\<アカウント名>\.nuget\Packages
As package source, every user will have their own version of packages which will be wasting storage space unnecessarily.
You can configure any path you want, add per your requirements.