You are neglecting the risk-factor of pulling in libraries from unknown authors on npm vs the stdlib. The package-bloat problem is one of culture, where developers keep neglecting this risk, only seeing the 5 lines of code they save by importing something, without seeing the potential cost and tech debt of having to review, maintain, update and security-monitor this dependency for all future.

Nobody thinks leftPad was not a useful function. The question is, was it useful enough to counter all the risks of npm, probably not. In the stdlib there is no such risk.