The problem seems to be a lack of education in many cases. I'm not criticising any one group but suffice it to say that some think that the gaining of a basic aviation licence of any sort is all they need; no more need be learned. I've been in the profession since 1971 and hold the view that if I learned nothing new on a flight it's because I'd stopped trying to learn. I won't ever stop trying to learn; if I do I'll give it up.
One thing I have noticed in some pilots is a lack of awareness about the true numbers of airborne traffic in Class G in UK. Some obviously think that lookout is the answer to everyone's VFR issues. From experience, it certainly isn't; the RAF taught us that in our early training. About thirty years ago a study was carried out (by RAE Farnborough I think) and the reality of the inadequacies of the human eyesight in the aviation environment is frightening.
As someone who tries to gain an ATC radar service where appropriate and as a long term TCAS/TAS user, I'm amazed by the number of other pilots who just don't comply with the rules of the air with regard to collision avoidance. I put this down to a failure of lookout on their part because I'm sure no-one would deliberately fail to take the necessary and mandatory avoiding action on another aircraft but many do fail to do so. I'm sure I've failed to see a few in my time too, see the previous paragraph.
These very same pilots who don't look out properly under "see and avoid", have no on-board collision avoidance equipment and don't think it a good idea to seek an ATC service are probably the very same ones who don't believe there is a problem. They fail to see other aircraft around them and therefore in their ignorance believe the sky is less busy than it really is.