WHERE clause does not find column after a CTE?

Question

New to CTE's and subqueries in SQL.
I have 3 tables:

categories (category_code, category)
countries (country_code, country, continent)
businesses (business, year_founded, category_code, country_code)

Goal is to look at oldest businesses in the world. I used a CTE:

WITH bus_cat_cont AS (
    SELECT business, year_founded, category, country,   
           continent
    FROM businesses AS b
    INNER JOIN categories AS c1
    ON b.category_code = c1.category_code
    INNER JOIN countries AS c2
    ON b.country_code = c2.country_code
    )
SELECT continent,
       category,
       COUNT(business) AS n
FROM bus_cat_cont
WHERE n > 5
GROUP BY continent, category
ORDER BY n DESC;

The code works without WHERE n > 5. But after adding that, I get the error:

column "n" does not exist

I realized there is a much easier way to get the output I want without a CTE.
But I'm wondering: Why do I get this error?