This depends on the file system in question, and how it organizes it's data on disk. Some file systems have a max limit on how many files can be in a directory

This depends on the file system in question, and how it organizes it's data on disk. Some file systems have a max limit on how many files can be in a directory, others have a max limit on files in an entire volume etc. Granted todays system are a bit more robust, but can be still targeted towards a variety of usage scenarios.