seroquel is generally better tolerated than other atypical antpsychotics, plus it is newer so docs are perscribing it a lot like other newer drugs.
it also has a better efficacy to safety ratio, and it is a good antipsychotic.
There's considerable controversy about the extent to which the manufacturer misrepresented its efficacy to safety ratio - that matter's being litigated now and the manufacturer has already been fined $530 million for pushing its off-label use for "minor" disorders (other manufacturers of atypical anti-psychotics have also had huge fines levied against them for the same practice).
I suspect that when the lawsuits shake out there'll be less doctors prescribing it as some kind of magic bullet for all mental health issues and more emphasis on using it only as an antipsychotic.