Brother. It is Google
More than showing you data of your website, it has more tasks on the primary basis.
Think about the number of pages available for a keyword.
Now if they tell you about your impressions of your website in SERP, it is a BIG thing. Even if estimated or a near about statistics, you shall be highly grateful to Google.
It takes huge DATA, database tables and money to bear all that which you get for FREE.
Now, keep calm, work hard and get clicks instead of impressions.
And use google analytics.
GA will also not show you the keywords very quickly. It takes time to update the data.
It is tricky mate.