They do not get sectioned for these reasons. They get sectioned because of a mental illness.
Yes, they are initially sectioned due to mental illness. If a section 2 lasts long enough (possibly due to lack of supported housing or waiting for a Tier 4 placement) it progresses to a Section 3. A section 2 runs out after a certain number of weeks.
Sadly MH issues often go hand in hand with housing problems. Few MDTs will discharge a vulnerable patient as street homeless! They might take them off their section and tell them to present to the council as homeless (normally they go into temporary accommodation/B&B via this route) but not if they are psychotic or risky.
Often people with personality disorders threaten suicide (due to emotional intensity or fear of discharge) yet their behaviour and attitudes may suggest they are not at risk. As an inpatient they are closely observed.
Many patients go AWOL and ring the ward after a few hours to say they need a taxi! The classic case of ‘if you discharge me I’ll take an overdose’ or inciting other patients to self harm or tie ligatures; this usually activates a rapid discharge via the PD pathway. Long hospital stays for these patients can be detrimental to their welfare (and that of other patients on an acute ward. If the team feel their risks can be better managed in the community they may discharge with community support.
Other people get stuck on a section 3 because they have no home or family to return to, but are considered too risky or vulnerable to discharge. Even if they are well after treatment, there is a risk of relapse. Especially as Covid has caused a lot of community services and support groups to fold. The wait for specialist placements and supported accommodation can be very long.
I thought the ward has a duty of care to inform police if a sectioned patient goes AWOL? What the police do with this information I’m not sure, it depends on the patient and their risks I guess.
Informal patients can be very unwell but if they agree to stay voluntarily they are not always sectioned. However they may not be granted unescorted leave and if they try to insist on leaving the doctors can put them on a 2 if they feel they are too unwell to leave.