The correct answer is "the population of the United States grew during those years".
Let's take the timeline of the House of Representatives number of members.
- In 1789 had only 65 members, the original House.
- After the 1790 Census, the House was expanded to 105 members.
- The number of seats increased to 142 members after the 1800 Census.
- The number of current seats (435) has not been increased in more than a century, even though every 10 years the census shows the population of the United States grows, because of the Permanent Apportionment Act of 1929, that is the outcome of a controversy between rural and urban areas after the 1920 Census.