One of the reasons Linux was perceived as more secure than Windows was because of the use of package managers, introduced in the early 90's if I recall correctly, to install new software. One of the many advantages of a package manager in this regard is that every package is monitored, and can be checked for integrity and other issues.
Whereas in Windows, for the longest time, people simply went online and downloaded the first link that they saw. In that sense, it's unfair to claim that Windows was more vulnerable than Linux because all operating systems are vulnerable to software than runs with elevated privileges.
The main difference is that on Windows, as you rightfully pointed out, there are things like Windows Defender running in the background and yet these things continued to happen. I guess that all these so-called security suites were just too busy stealing the user's data for themselves to notice the real malware threat (funny how "malware" is such a relative term).
So much for *cough* real-time protection. 1 2 3
Password-stealing Linux malware served for 3 years and no one noticed
In Linux, as mentioned, it's standard practice to use the package manger available in order to download and install new software. This alone explains why it took so long to notice the issue. The same type of careless people who do this would also be careless about verifying the downloaded file for integrity and known malware signatures.
To their credit, the authors of this gimmick were smart enough to use a probabilistic mechanism to deliver this payload randomly, as opposed to consistently which would have made it easier to identify.
It's not too late to check if a Linux device you use was targeted.
No device was targeted. The user needed to go to this particular website, download this package and explicitly run it and accept the prompt to run with elevated privileges. It does not imply a security vulnerability on Linux or any other operating system.
I completely agree. Even in these forums we're already seeing more activity from people who are moving away from Windows. Unfortunately, not everyone has the same willingness to put in some effort to learn and adapt to new environments with different tools and procedures.
Poor security hygiene habits cause the amount of infected devices malware to grow. It's actually very similar to how real world diseases spread: careless people with poor hygiene and sanitary habits blending in the crowd, unaware of the damaged they are causing.
As more people start using Linux, which I generally see as a good thing, we're also bound to see rising numbers complains about how Linux is not Windows and how we need better alternatives. For free. 
