As a supplement to @TheIronCheek's good answer:
According to the Legends Wookieepedia article on blasters, firing the blaster imparted a significant amount of heat to the weapon. From the article:
A side effect of firing blasters was the gas conversion enabler heating up as gas was energized by the power pack, which could cause blasters to overheat, sometimes to the point of destruction
While I couldn't find anything specific on blaster heat in the Disney canon, I think it's not an unsafe assumption that heat could still be an issue for weapons in the Star Wars universe.
Therefore, from a design perspective, something that must be addressed by blaster designers is how to handle heat. How well the blaster can handle the heat from firing will determine its maximum firing rate. Take, for example the DC-19 "Stealth" Carbine:
...the invisible tibanna mix had to be reloaded after every ten shots, and
there was a required cool down time between each individual shot to protect
the blaster's dampeners from overheating
Now, all this is Legends material, so take as a piece of canon evidence for blasters producing heat the Z-6 rotary blaster cannon. One way to get around the heat problem as a weapon designer is by adding more barrels, hence we got (in our galaxy) the Gatling gun:
Gatling's solution was to utilize revolving barrels-four on some early models,
six on most Gatling guns, so that each barrel had an opportunity to cool as it
revolved. Numerous rounds passed rapidly through a rifled barrel cause a
tremendous heat build-up.
Therefore, the existence of the Z-6 in canon suggests heat management reasons for having a rotary barrel on what amounts to a rapid-fire blaster. Or, it's just the Rule of Cool.