they were retconned into plasmaguns yes, but they were originally sold to the audience as lasers.
Actually, the most usefull explanation is a gas-induced
Soliton wave.
It explains why the turbolaser can do damage before the visible part hits (the soliton wave travelling at (near) c, the gas at slower speeds), why they are not affected by gravity, how they can contain so much energy (GT-range for heavy TLs) and various other strange behaviours.
The turbolasers were never "sold as lasers", except for the part of their name. Well, names do not mean much - or do you assume that "plasmacannons" are firing cannonballs that turn into plasma?
We never know the exact physical properties of blasters, lasercannons and turbolasers (all operatin on the same principles).
We know that they fire some kind of "blaser gas", that the visible part of the beam travels at sublight speeds, that they are not significantly affected by gravity and that the visible part has negligible spread/bloom over long distances.
Lasers (light) do not behave in such a way.
Plasma does not do this, either.
But a gas that is heated into a plasma and ejected from a specialized barrel (which might or might not modify it further) so that it creates a solition wave that moves independently of the gas can explain all of this.