The local / regional approach

We know that there are legal aid deserts around the UK, where free legal advice is not available. The Law Society and Lexis Nexis have produced some maps showing areas with and without provision (in England and Wales).

There are also areas of advice drought, where advice appears to be available but, in reality, is extremely hard to access.

Why do some areas have apparently robust provision in one area of law, but little or none in another? Why do some areas have persistent advice deserts across most or all areas of social welfare law? Are the barriers to provision the same across all areas of law, all parts of the UK, and all regions and sub-regions of each jurisdiction, or are there some place-specific barriers?