If you go to http://www.google.com, you will be redirected to https://www.google.com. Notice that Google moved you from http:// to https://.
Information send over HTTPS is a little slower that what is sent over the normal unsecured protocol HTTP; this is because of the time it takes to encrypt and decrypt the information that is being sent and received. Then, why are these popular websites moving to HTTPS, away from the normal unsecured and faster HTTP protocol?
Millions of persons are using wireless devices (Wi-Fi) to connect to the internet. A Wi-Fi device uses radio waves to transmit data between itself and the device that is connected to it. These radio waves can be intercepted; the data it carries can then be viewed and used for scamming and hacking purposes. The technique is called Wi-Fi snooping. If you are using an unsecured wireless device at a coffee shop, the airport or any Wi-Fi hotspots, someone may be spying on you. Someone with a Packet Analyzer Software will be able to view the contents of the webpages you are viewing.
In order to prevent someone from spying on you over on unsecured wireless connection, the data sent and received must be encrypted; this is where HTTPS comes in. If your data is encrypted, it can be intercepted but, will not be able to be viewed or understood.
Here is a video of someone showing you how he can spy on a person using an unsecured Wi-Fi connection and login to that person’s Facebook account.
So, the reason for switching to HTTPS is to protect the millions of users these popular websites have from Wi-Fi snooping, who are using unsecured wireless connections at coffee shops, airports and other Wi-Fi hotspots.