Parshanut sobre Números 26:67

They numbered. The early commentaries expressed astonishment as to why the tribe of Levi was smaller in population than the other tribes. In my opinion, the answer is that “by Him actions are weighed” — and He knew that the tribe of Levi would be the King’s legion. They would not inherit a portion, only the cities of open spaces. If the Levites would be numerous, they would have a complaint: Why was their inheritance reduced? Additionally, Bnei Yisroel would find it difficult to support a large population. Therefore, the Creator saw fit, in His wisdom, to withhold the miraculous population increase from them, and they only increased in a natural way. They were not counted among Bnei Yisroel, since no inheritance was given to them among Bnei Yisroel — therefore, they were less in number.