The "security line" is not simply a question of "doing a lot" and "giving a lot back", ex post facto, or setting an "example" in the "security industry".
It also has to do with design goals and priorities. Layer upon layer of cruft, with an OS weighing in at multiple GB, is not a confidence builder in the "security line". It also includes default configurations.
There are reasons that so many Windows instances have been and are now part of botnets. There are reasons why the security updates have increased in quantity and frequency over the years and appear to be neverending.
Some of those reasons have to do with design and priorities. Others with default configurations that Redmond assumes no user will ever change.
No amount of PR can change reality (e.g., massive botnets of Windows users), although it might change people's perception of reality.
Also, I never said "major competitors". I said "other OS". For example, the OS I use is probably not a "major competitor". It is much smaller and open source. That is what is important to me.