Most people don't have a solder iron and the skills needed to pull it off.
My guess.
Yep. That would be true.
If you want it done right the first time, do this.
Get the right size of spade/blade crimp-on connectors separately for the + & - terminals. Most auto supplies carry them on the shelf. All car stereo places carry them. Or get them thrown in the bag for free when you buy the speakers.
Throw away the insulator that comes on the crimp. Crimp 'AND' solder the connector onto the wire. Heat shrink over the wire end and connector junction.
The correct size of spade with a very fine barb will just lock into place. It should not come free unintentionally.
Sometimes you need to strain relief the wire against shock and vibration. Many speakers have this provision built into the speaker basket.
Why not solder the wire directly to the speaker terminal? Many reasons.
Serviceability. Do you really want to unsolder and re-solder the speaker terminals if you need to R&R the speaker for testing or access.
Over heating the fragile phenolic, plastic, or pressed paper terminal bridge can loosen it from the speaker basket. For the same reason (it melts the surrounding plastic) you never solder onto an enclosure terminal cup.
Over heating the terminal can loosen the terminal.
Over heating the terminal can cause the braided tinsel lead to conduct solder and lose its compliance over a portion of its length.
Under heating creates a cold solder joint and poor conductivity.
Boat building standards discourage any soldered termination when that termination is immobile, like into a circuit board.
With a little experience and a pencil tip solder gun (not that big pistol gun or small torch) you can master this with no problems. Why take the risk. Do your soldering on the removable connectors.
