Committee assignments are granted by seniority, so it’s advantageous to have legislators with a lot of seniority.

In the Senate, West Virginia had Robert Byrd for basically forever — he was the longest-serving senator in American history, died in office — and so he got to lead the Appropriations Committee, which gets to direct money places, which is a pretty desirable spot.

https://en.wikipedia.org/wiki/Robert_Byrd

Robert Carlyle Byrd (born Cornelius Calvin Sale Jr.; November 20, 1917 – June 28, 2010) was an American politician who served as a United States senator from West Virginia for over 51 years, from 1959 until his death in 2010. A Democrat, Byrd also served as a U.S. representative for six years, from 1953 until 1959. He remains the longest-serving U.S. senator in history; he was the longest-serving member in the history of the United States Congress[1][2][3][4] until surpassed by Representative John Dingell of Michigan.

Byrd became West Virginia’s Senior Senator in 1985 following the retirement of Jennings Randolph. He served three different tenures as chairman of the United States Senate Committee on Appropriations, which enabled Byrd to steer a great deal of federal money toward projects in West Virginia.[9] Critics derided his efforts as pork barrel spending,[10] while Byrd argued that the many federal projects he worked to bring to West Virginia represented progress for the people of his state.

https://en.wikipedia.org/wiki/Seniority_in_the_United_States_House_of_Representatives

Committee leadership in the House is often associated with seniority, especially in the Democratic Caucus. The Republican leadership, in comparison with the Democratic Party, prioritizes voting records and campaign fundraising over seniority for committee leadership.[2] Party leadership in the House is not strictly associated with seniority.

The more senior a representative is, the more likely the representative is to receive desirable committee assignments or leadership posts.