There are numerous reasons that can affect why your site may not be first in Google.
Even if you have a checklist of all of the known SEO ranking factors and you have worked through them all; there is still no guarantee that you will rank 1st.
The most commonly forgotten factors are:
We also have to remember that SEO takes time. Most SEO analysts will say 4-6 months until the client sees a difference in ranking, and even then, that’s just a difference. In order to rank highly in competitive areas, this can stretch to a year to a number of years. As long as you can see consistent positive movement then you can be assured that the SEO is working.