I have a theory. in "normal" deaths there's usually something that can be blamed, be it directly or indirectly. so people find closure in anger against that source and then they move on with their lives once they rationalize it.
death is extremely traumatic for us humans since we tend to ruminate on the past and be very attached to others, that's just the way we evolved.
But with suicide this is different, the people mourning have nothing to blame other than the person who committed suicide or themselves, after all, there must be a reason why they killed themselves, and they star thinking was it because of me? was it others?...was it really my fault?
and this is what creates such strong feelings. of course this is different for everybody, but that's what I've seen when a suicide occurs and why it's so hard to move on from a suicide. there's no clear victim and it's hard to find perpetrators, that's also why some parents of people who killed themselves campaign against pages like this, they identify it as the thing that took away their loved one.
this is a complicated subject and i'm sure that there are a lot more factors and reasons why this seems to be the case.