Large templates are difficult to troubleshoot. This is a known fact. The larger the number of resources in a template, the more difficult it is to troubleshoot the template. A template deploys all resources in it, and finding a bug involves deploying the template quite often. Developers would have reduced productivity while waiting for the completion of template deployment.
Also, deploying a single template is more time-consuming than smaller templates. Developers have to wait for resources containing errors to be deployed before taking any action.