Mental health issues is cause for concern for property damage. Speaking as someone who has them and has had a helluva time getting it managed.
It also means that if the tenant does undo damage the landlord is less likely to get any money back. (the tenant has none and the government won’t cover it) Plus in the situation of eviction, the council will usually explicitly advise the tenant to stay and make the landlord go through the time and expenses of court. A wealthier tenant is more likely to have the means and willingness to just move.