It’s an abuse of a rule meant for something else. There is no reason it has to be 60%

The rule comes from a bit of Senate procedure where you vote for “cloture”. What this is supposed to be is “we’re done discussing things, and now we should move on to voting on the legislation”. It’s not supposed to be a vote for or against the legislation itself, but rather just moving along in the process.

Over the years, it got abused more and more to mean “a vote for cloture is a vote in favor of the legislation”. Around the time Obama started his first term, it fully meant that.

The Senate can simply change the rule to require majority vote. It would require a simple majority vote to do so. There’s a lot of fossilized politicians on both sides who don’t want that. They know that America tends to be swingy with its votes; the party out of power now will tend to be the party back in power next cycle. They want the power to stop legislation when the cycle swings against them.

Now, if Republicans in the Senate believed they would have a permanent majority through vote rigging, which is clearly the Administration’s plan, then they should have dropped the filibuster rule like Trump wanted. The fact that the idea was stillborn suggests that congressional Republicans don’t actually think Trump can pull it off, or perhaps that the plan wouldn’t benefit them individually, or they are somehow not in on the plan.