As a NY’er, Chuck Schumer brings home enough Govt regulation, pork and money to satisfy his key constituents - the Gov’t and teacher’s unions, and those who benefit from big Govt. Besides that he makes efforts to appear “populist enough” to cater to NY City and surrounding county lefty or working-class voters.
Upstate voters outside of these groups never vote for him, but they don’t, and never will, have enough numbers to matter.
I actually believe Chucky’s seat is become safer. As population flees the State, it increases the relative percentage of his supporters.