Speaking specifically for Ireland, there are two main causes of homelessness.
The first is the opioid abuse epidemic in Dublin. A large proportion of people on the streets suffer from substance abuse problems. Most come from poor backgrounds, possibly domestic violence and abuse, and fell through the cracks. Very sad...

Then there are people who lost their homes in the 2008 global economic crash. A lot of people who got mortgages before 2008 ended up paying bought homes that were way overvalued, and ended up in negative equity. A lot of people lost their jobs or had wage reductions due to austerity and their homes were repossessed by the banks. The banks themselves were of course bailed out by tax payers to ensure that foreign investors and bondholders in the Irish property market casino didn't lose any money. This category was less likely to end up on the streets, many ended up staying with friends, family or in some cases the government had them reside in hotels.It was, and still is quite a mess.

While there is a government housing list, families and single mothers with children are prioritized. Men, especially single men are very low priorities and are unlikely to ever get government social housing.