Why is Tom DeLay such a powerful figure within the House of Representatives? Why was he, and not some other Republican member of the House, elected Majority Leader? Is it seniority?
Partly seniority, partly other reasons. Congressional rookies tend not to get elected Speaker, but just hanging around long enough won’t get you the position either. You have to demonstrate serious ability to fundraise, to count votes, to use carrots and sticks to get the votes you need and demonstrate general leadership abilities within your parties. You also need to be loyal to the party - mavericks tend not to make it.
DeLay served as Majority Whip for 8 years before becoming Majority Leader. During that time, he demonstrated a capacity for basically getting shit done. Say what you will about his value, but the man was a workhorse during that time. He was also adept at maintaining party discipline and earned himself the nickname “The Hammer.” He’s very good at rewarding “good behavior” and punishing bad.