Actually, sometimes some users do know that they are spamming, and they know it must not be allowed, but they still do it. I don't know whether they enjoy doing it or they simply lack basic knowledge and don't know anything about what is being discussed or what others are talking about, but they just say whatever comes to their minds.

You can also often find trolls and serial spammers who will go into different threads and sections and post against OPs of different topics only to troll them and you will find them making no sense at all. This is also a sort of deliberate spamming that you can witness in the forum very often.

Other than that, you did a good job by compiling this list, and if newbies read it and pay attention, they might learn a thing or two about what they shouldn't do for them not to become spammers.