Small guns often have problems because:
1) As GeorgeH has put it, it is easier to build a clock than a watch.
2) Few companies even make the attempt for reason #1.
3) Most companies that do make the attempt focus more on keeping price down than keeping quality, reliability, accuracy, and durability up. The only ones I know of that really focus on quality are Rohrbaugh, North American Arms, and Seecamp, not suprisingly companies that focus solely on pocket guns. A good case could be made for Kel-Tec, which although inexpensive and with variable QC, can be made into quite a gem with the right parts substitutions and customizing.
4) We now have .32, .380, and even 9mm guns that are the same size as or not much bigger than .22 and .25 autos of the past. The innovators are really pushing the power/weight ratio into uncharted territory.