NIT Raipur has not been ranked in international rankings because it still hasn’t reached the level where ranking bodies would consider it credible enough to be ranked. They consider a number of criteria while evaluating colleges such as Employment Reputation, Ph.D. faculty, Citations per faculty, Intentional students, and Intentional students. Sadly, NIT Raipur is way behind other NITs at least on the basis of the aforementioned criteria.
Here is a short comparison between NIT Raipur and NIT Rourkela that will help you understand this better
The above-stated points prove further why NIT Raipur hasn't been included in international rankings yet while NIT Rourkela has.