Because they sell a print copy of the rules and would like you to buy those.
If your buddy has a copy and you have a PDF I don't see what the issue is. You can read the PDF and he can bring the rulebook to games. If that turns out to be a PITA then the book is pretty darned cheap and very nicely put together.
As has been mentioned, you'd burn through more money in ink printing the PDF off so if you want a printed version you're better off buying a $15 copy of the rules. It will also be printed in a much higher resolution than your home printer can handle. So all in all a much better deal.
Instead of complaining about the lack of print functionality in the PDF you should be happy that the PDF even exists. In two versions no less. Most companies do not even provide any sort of free PDF for rules that they sell so Wyrd is certainly extending their fans a courtesy that almost no other company does.