Why is it still passing so easily? (72-23-5)
I'm not sure where you saw this vote total. Most of the things I've read suggest that it was passing with only a temporary extension if at all, though most suggested it was also gridlocked.
What you need to know is the following:
It's a vote on Section 215 on the Patriot Act specifically, as far as most are concerned. That's the one that the NSA has used to authorize the mass phone metadata surveillance.
The decision is not just "reauthorize or let it die". There is a proposal in the Senate and House (which passed the House) that would alter the Patriot Act to allow the phone companies to store the metadata, which the government could only access with more specific requests for information.
You can read the USA Freedom Act information here, or a commentary here (as well as various places on the Internet).
The Senate is having more trouble primarily because of the composition. GOP candidates running for the nomination cannot go against the concerns of Republican primary voters, whose top issue is national security. This is being painted as a way to ensure national security, so some GOP candidates (Rubio and Graham) are pushing it. Others, like Cruz and Paul, are pushing against renewal but may go for the USA Freedom Act if pressed.
Yet another problem is the way the House and Senate work. The House leadership agreed to the USA Freedom Act as a compromise measure, and the House essentially doesn't allow filibusters. In the meantime the Senate has McConnell in support of the Patriot Act as it stands, and filibusters are possible, so each person has more leverage and can get what they want.
Politically speaking, in terms of the favorability of reauthorizing the Patriot Act, Senators can't hide from their state constituencies even if there's national cover. While the ACLU commissioned a poll showing that 60% of Americans don't believe that the Patriot Act should be reauthorized in current form, that's not to say that they agree on what alternative should be implemented. That's also not to say that Kentucky voters, who elect McConnell for example, don't feel more strongly that it should stay as is. Perhaps it would be a huge problem for some Senators to vote against the Patriot Act in current form because it's a big issue for Republican voters in their states.
And finally, there's one more problem: personal belief. It doesn't always matter about political cover. Maybe these Senators actually fully believe that they are in the right in trying to reauthorize the Patriot Act, and have judged that the political fallout would not be as bad as the failure to reauthorize. Some Senators do lead, rather than just blindly act as delegates for their constituents, which is part of why we have a representative democracy.