Linux’s user base is small, so it isn’t a very attractive to malware developers.

Linux’ user base is huge and there were lots of malware for all kinds of devices, e.g. Linux routers. I think what you meant was that the market share for GNU/Linux on desktop devices is pretty small.

Linux’s userbase is mostly tech savvy people, who don’t do stupid stuff.

Both of these assumptions are false:

• There’s a difference on being an active administrator of a Linux system and not even knowing you run Linux.
• Tech savvy people do stupid stuff all the time, just nobody catches them doing it because most of the time they don’t go around telling people (they can usually fix it themselves).