Why aren't the calendars I can see on my iPhone in GCal for Google Calendar?
On iPhone, Google have a specific app different from their web version. With this specific app, Google is able, basically, to merge all the accounts in 1 view. This feature is not available on the web version, on which GCal is based on.
Hopefully there is a lot of options to achieve the same result. Check the questions below to know more.