I'm not sure, maybe because that's what they had back in the day when it was made. 
It certainly is reliable.! 

How odd, I wonder why they would use a resistor instead of a choke. Although I have seen similar things done for spectral lamps so maybe it's more preferable for scientific applications, who knows.

No this is the AC one. 

300C? My gosh that's like soldering temperatures! I suppose this runs on DC instead of AC, so resistance is (was) the only option for current limiting.

And that photo is probably the first and last time it will be seen clean and tidy

Also, the resistance gets rather warm (around 300℃ eeeek...!) so leaving it on at this time of year isn't exactly comfortable, this is definitely a wintertime lamp

We had our AC Point-o-lite litted this evening, not for very long, as we want to preserve the lamp for as long as possible, it was in a right state when we go it, and were remembering that the seller was chuffed that we'd chosen to restore it rather than 'upcycle' it.! 

It's been a long time in the making, I've had the wood to make it with sitting by the front door for almost a year.! But now the new workbench has been completed, and though there are still a couple of finishing touches to be done it's in use and is an improvement over what we had before. 
At the left hand side of the bench at the back are three double gang sockets fed directly from the mains via a 13A plug, and at the front is a vice that Ria has had for as long as she can remember. 
Also at the front, using our 110V DeWalt router I've inset a 24" steel rule. 
At the back there are two Ethernet sockets that are plugged directly into the router, one is for guest access, that can only see t'interweb, but the second one can see our home network. 
At the right hand side of the workbench are two double sockets with red switches that are fed from the Variac and there's a power meter in line with them. 
There is also an isolating transformer, essential for powering kit when using the silly scope and three quick test blocks, 13A, 5A and US.
Right at the top is a 12V power supply feeding a US spec inverter, which we use for our US lamps, and our silly scope and function generator.

Well it's finally in print and here it is.! 🐵🐵🐵

I'm afraid you lost me by about the 2nd line 

Hopefully Max or someone else with more brain cells than me reads this..!