The main reason why this is true can be found in the number of members in the two houses. The Senate only has 100 members and so its members can (potentially) function more like a group of friends and colleagues.The House, with its 435 members, cannot work on personal relationships.This same dynamic is helped by the fact that Senators serve for 6 years.This tends to give them more time to get to know one another.
The Senate can function effectively even though it is rather informal.This is because its members know each other better and have more personal relationships.
Hope this helps!
