Yes, they should do everything over HTTPS. I assure you they're moving in that direction, but they have thousands of pages and many different rendering technologies to deal with (after 20 years, some cruft and fragmentation is par for the course).

However, this article insinuates that HTTPS is enough to hide from the government. HTTPS only protects data in transit. If the big internet companies are complicit in leaking user data to the government (as Snowden showed) then HTTPS isn't going to be useful in that regard.