Why is no one signing their emails?

PGP could also be used; we can bypass much of the key exchange dilemma by just shipping email clients with keys for large organisations (PayPal, Google, etc.); like browsers do with some certificates. Well, by not having glaring stupid spelling errors, duplicating the PayPal layout in emails, duplicating the PayPal login screen, a few forms, and getting an SSL certificate. Banks, financial services, utilities, immigration services, governments, tax services, voting registration, Facebook, Twitter, a zillion websites … all happily sent me emails hoping I wouldn’t consider them spam and hoping I wouldn’t confuse a phishing email for one of theirs.

Source: arp242.net