Its because of file ownership
When you list a directory you see something like snapey snapey against each file or directory which means that I own the file and the file belongs to the snapey group.
The permission 750 says that the owner can read, execute and write, group members can read and execute, and all other users have no access.
The permission 755 says that the owner can read, execute and write, group members can read and execute, and all other users can read and execute.
Assuming your web server is running under an account like www-data and is a member of group www-data then with 750 it has no rights to access snapey's files.
You can change ownership with the chown command, for instance chown -R www-data:www-data public_html would change the ownership so that the folder and all its children (-R) belongs to www-data user