>Why would a program running in Linux are more altruistic (for lack of a better term) than one running in Windows?

It's an entirely different culture. Windows users are used to paying for software (starting with the OS), and Linux users aren't. So the monetization strategies are different. For Sublime, that seems to be primarily a Windows program that tried to cross over, so it's not surprising it would reflect that history.

I did say "offhand"; I'm not personally familiar with npm. There is some stuff like this in Linux-land if you know where to look, of course, such as the message in Vim, but even there you only see it if you start the program without any filename argument, or look in the docs, so it's hard to call that "nagware", which usually means something that won't allow you to use the software without first reading and acknowledging the advertisement.