One of the biggest limitations of the matchlock was the need for a permanently-lit, smouldering cord to set off the priming charge. Also, balls and propellant were not packed into single cartridges, but in pre-measured wooden vials that were tipped into the barrel, with the pan primed by loose powder from a powder horn. Thus, with so much loose powder and lit matchcords going around, musketeers armed with matchlocks inevitably had to be widely separated from each other and follow a long series of detailed words of command to avoid the possibility of misfires or accidental explosions. Consequently, the rate of fire of matchlocks was glacial, offering only about two shots every three minutes. That limitation and a shortage of matchcord material in Sweden led the army of Gustavus Adolphus to adopt the snaplock, a primitive form of flintlock that used friction to generate sparks to set off the priming charge. That allowed musketeers to be arranged in much close ranks, thus increasing the density of their volleys. The transition to the flintlock in all European armies was almost complete by 1700 (though the French seem to have been inexplicably reluctant to adopt it). Another innovation that went hand-in-hand with the flintlock was the paper cartridge, which packed both powder and ball into a single unit that could be used to both prime and charge the weapon without all that tedious mucking about with separate powder-measure vials and a powder horn. Consequently, the flintlock had a much greater rate of fire of around two rounds per minute, and up to three in the hands of a skilled user.

Sources:

Allan Mallinson, The Making of the British Army

Paul K. Davis, Masters of the Battlefield