Sometimes we have to retire things due to manufacturing issues, supplier issues, shipping issues, legal issues....I'm guessing this one fell under one of those categories.

Some electronics are so sensitive that they have temperature limits. They'll usually say something like: "do not exceed solder temperature of 270 degrees for more than 3 seconds". The problem being that different solder has different melting points and solder just behaves differently at different temperatures. Some solder burns up at 350 and some will barely melt. Data sheets for components usually have a list of maximums and minimums.

90% of the time I set and forget the iron at around 300-320C. This is a good range for me for standard PTH and SMD soldering. I've had a few occasions when I need to really increase the temp to the 400-450 range; usually when soldering large gauge wires with a lot of thermal inertia.

The same reason you'd want a variable temperature* soldering station; A common use case is when you have to work with both leaded and lead-free solder, the latter typically requiring higher temperatures which in turn can make working with leaded solder a potential hassle (especially if it has a flux core that burns up rapidly at higher temps).
*However, I think mostly the difference is that a non-variable unit is often also a non-controlled unit. I.e. the 25W goes in, heat goes out, and what temperature that ends up being (due to ambient temperature, the part being solder, etc.) is not actually considered.

Approximately infinitely better. If left alone the firestarter just keeps dumping energy into the tip until it burns everything it touches (and itself), whereas temperature control is better for sporadic use while powered.

Worse iron holder. Also, potentially lower thermal mass in the iron itself (since the electronics are in there as well).

I just tested out a few tips from the Hakko T18 series. They fit like a glove.