Question

Why is cloture very difficult to achieve?

Senators are famous for their debating prowess and would not easily give up to cloture.
The two-thirds vote of the Senate is almost impossible to attain.
Cloture can only be achieved by a three-fifths vote, and parties don’t usually have that kind of majority.
Senators usually wish to continue the discussion, and work hard to prevent members from voting for cloture.

Answer 1

Cloture is difficult because it requires a supermajority — three-fifths of the Senate (normally 60 of 100 senators) — and parties rarely hold that large a margin. (Historically the threshold was two‑thirds; it was lowered to three‑fifths in 1975 for most matters.)