Thanks to the idiotic way the Senate is made up.
The 50 Democratic Senators represent 41 million more people than the 50 Republican Senators. Our system is broken.
I can understand the frustration because we don't have a super majority but that the Senate is only 2 people per state each placed within 1 of 3 classes that are staggered so no more than 34 (currently, based on our # of states) Senators are ever up for re-election is important.
1) It means the Senate is immune to gerrymandering, because Senators aren't decided by districting but rather the whole state. This is only possible because so few people are elected with the classes spread out between each senator in each state so at any one point and time only 1 person from a state is every up for election if a state has a senator of that class. The system would fall apart if you added more senators to each state and would essentially necessitate districting to have a reasonable voting process which leads to gerrymandering.
2) Because the Senate represents the entire state, Senators in most states actually have to represent their state well. Since Representatives represent a district and not the state, and the district was likely gerrymandered to favor them, they can easily be a little more...extreme...and get away with it.
3) Because Senators are elected by the whole state, statewide efforts to get people to vote are more important, and policies or PR that hurts a state can change it. Without how Senators are elected, AZ & GA would not be full blue right now. A Democrat Senator in West Virginia would very likely not exist without the current system, either. (because he'd be districted out of running with the GOP legislature in WV)
3) The nature of how the Senate works benefits having less people rather than more. Easy examples of things that would be immensely worse with way more people include filibustering, impeachment trials, election certification (remember this years??? imagine that with 300+ more people each with the potential to delay it further. big yikes.), cabinet/judge appointment hearings, budget reconciliation deliberation (the stimulus check plan about to be deliberated on here), etc. The Senate naturally has the jobs that require the most focused discourse and deliberation, so tons more people would exponentially slow it down.
Case and point, the worst people in the Senate at this point is Hawley and Cruz. They suck, don't get me wrong (especially Hawley), but neither of them are anywhere on the level of Greene or Boebert in the House. A Greene or Boebert in the Senate is near impossible since they would need to win statewide agreement, essentially, whereas in the House it's not difficult if the districting favors QAnon supporters or extremely low educated voters.
You don't want the Senate to work anything like the House does.