It’s because they use 2 different SSL certificates , there are 3 common certificates that we are now using now
DV ( Domain Validation ) is the most common one, it’s very cheap, easy to order. The CA will verify your domain, make sure that you are the owner of that domain by sending a verification email to your admin email contact on whois record or some other method. OV (Organization Validation) – is mostly for corporate , the CA will not only verify you are the owner of the domain, they also ask you some paper to verify your business address.
EV (Extended validation) – is most common for eCommerce websites, once this certificate is installed, a small bar displaying your company name + pad lock will be displayed on the address bar. EV Certificate is more expensive, there are some verification process to be taken.
Here is how the EV Certificates look like in some common browsers:
