Not everyone is able or willing to buy a house. House ownership is a middle-class concept which Maggie Thatcher wanted to extend downwards. As a theory it would indeed be wonderful if everyone owned their home and were able to maintain it themselves, but in practice it is not so simple. People may have no savings for a deposit, be insecure in their employment, not confident that they will be able to keep paying a mortgage, uncertain about whether they will stay in that area and unwilling to have all the upset of selling and buying elsewhere, or just not want the responsibility of all the details that follow from owning.
In other countries, the balance between owning and renting is not the same as in the UK.
If you don't own, the alternative to council houses social housing is private rental, with a huge variation in rent levels and quality. Social housing at known rents is standardised and maintenance is guaranteed, and moving to another town is relatively easy, you can arrange a swap with someone who wants to move to your town, (with LA approval).