It's not.
The filibuster is designed to give the majority party a permanent excuse not to pass legislation that their voters support but their financial backers oppose. It's been that way for years.
And I can guarantee you that if the Republicans somehow ever managed to get 75 seats in the Senate, they'd suddenly come up with a reason "based on historical principle" to change the Senate rules so that 80 votes are required to end debate and vote on a bill.