If they are having 300 cricket clubs is it hard to find some good batsman among these players, they lack a good batsman in the team to perform consistently and i think all these clubs prefer T20 and hence they are good at the shorter format.
300 is still a very small number, when compared to the other countries. For example, in India you can find thousands of cricket clubs in any of the major cities, such as Delhi, Mumbai or Bangalore. Another thing is the quality. I am not sure about the quality of the game, including the pitches in which the matches are being played. As far as I know, there are only a handful of turf pitches in Afghanistan. However, many of these clubs travel to the neighboring Pakistan to take part in various competitions.
But earlier the Afghanistan team was more balanced. They had good pace bowlers such as Shapoor Zadran and Dawlat Zadran, and the opening duo of Mohammad Shahzad and Javed Ahmadi was skillful. Even in the spin department, they had more variety with the leg spin of Samiullah Shinwari. Now they are over-dependent on the spinners (Rashid Khan and Mujib ur Rahman) and in batting they are too much reliant on Mohammad Nabi and Asghar Afghan. And this has affected the team balance.