Why is it a generally held belief that ToadyOne doesnt do any optimization as he works?
Because DF still has FPS problems. Also, new features tend to increase CPU load on average.
FPS issues will always persist though. A larger enough and or old enough fortress will slow down any computer.
Yes, but the whole point is it doesn't have to be that way.
So, you're saying that that dwarf fortress can be infinitely large (in terms of item count and embark size) and old?
Not "infinitely" large, obviously, since the universe can't do infinitely large, but sufficiently large such that the average modern desktop would have no problem with thousand year embarks bigger than anyone could possibly ever want.
Either you are unaware of the sheer complexity of DF or you think everyone has supercomputers. And that DF is multithreaded.
No, no, and no.
You're overestimating the complexity of DF and underestimating modern computing power and, most importantly, the benefits of algorithmic improvements. Keeping track of millions of objects and updating their positions, checking for collisions, updating various states, etc. is not as big a deal as you seem to think it is. Temperature, fluid, and weather simulations need not grind FPS down significantly at all.
Even if it was multithreaded, again, even in the best possible imaginary case, that wouldn't yield speedups of more than 2-4x for most people, which is nothing. It's great if you have nowhere left to go, and you want a more responsive UI, but otherwise not usually worth the trouble for most applications.