Sole practitioners face burdens that many of us do not dream of. In economic terms, those burdens revolve around the concepts of economies of scale, the corresponding disproportionate burden that regulation inflicts on smaller units, and the low margins inherent in providing retail services. To put it another way, lawyers with individuals as clients face many of the same costs faced by big-firm lawyers, but cannot spread those costs over a large number of lawyers, and cannot charge as much for their work because their clients cannot afford to pay large fees. Thus they are squeezed - and every increase in their costs will come directly out of their own pockets. Since costs are going up constantly, many sole practitioners are finding it harder and harder to stay in practice.
Computers provide a good example of the problem.
In years past, law was not a capital-intensive business. A large firm can spread many of these costs over many attorneys. A small firm or sole practitioner cannot, thus driving up their costs per attorney. The increasing regulation of lawyers is an even better example. Regulation adds greatly to costs, and while those costs affect all lawyers, it hits sole practitioners hardest.