It used to be that first class mail was available as an option for smaller lighter books... those under 8 ounces or so--on the pbs website.  I only see media mail now.  Why is that? 

the postal rate for 1st class has gone up. !st class costs more than media mail for many weights. 8 oz. first class costs more than media mail.

You can still choose first class. I do that quite frequently as it is only a few cents difference.  But it costs you $2.67 instead of $2.63.

There is a difference between 1st class envelope and 1st class package.