If you go back a very long time, say before the Civil War, windows were made locally, like just about everything; so the type of wood used varied. With the advent of industrial scale manufacturing in the late 19th century, white pine became the preferred wood for windows. It came mostly from Lake States forests until after the First World War. Pine production shifted to the West Coast and the window industry shifted to Ponderosa pine. There are some amusing exceptions. Railway coaches used cherry for window sash for its durability and stability. The German window industry prizes western hemlock from British Columbia for tilt and turn windows. It is specially milled and dried for them at great expense. I ran some cypress sash a long time ago, and it was a very nice wood to work with.
Trees from "old growth" forests--what foresters refer to as "first forest"--are very large, grew more slowly due to the shade of older trees, and have more clear lumber in them. These have all been cut down except for a few in protected areas. The last mill I knew of that cut old growth white pine was in Sault Saint Marie, Ontario. I bought pine from them into the 1970s. It was the nicest stuff in the world to run past a cutterhead. I shifted to what the lumber dealer called "soft textured Ponderosa" which I think came from higher elevation forests. It gave a slightly rougher cut which I attributed to greater contrast in the hardness of the early wood and late wood. The last really nice wood I bought for sash work was California Sugar pine around 1995. This was clearly old growth stock--2" thick, 12"-20" wide, 16' long, clear lumber. Those trees could be gone by now also.
With a few exceptions, most species of wood deteriorate when exposed to exterior moisture. Exterior durability is a desirable trait that contributed to the early over exploitation of those species. For a long time wood windows have been treated with preservatives to prolong their service life when exposed to weather, so compatibility of wood species and treatment method are important. The combination of white pine and pentachlorophenol was great while it lasted. Penta is a ferocious toxin and was banned about 1990. I worked with one manufacturer that was using a pressure treating process that made pine remarkably durable, but I'm not sure if it ended up being economically feasible. I still use zinc naphthenate from time to time.
So, you can't get wood like you used to. The wood window industry, like wood using industries in general, have put a lot of ingenuity into building better products with lower grade lumber.
I've been asked to make some replacement sash for a 1890 vintage building. I can't find the 8/4 white pine within 200 miles, so I think I'll be face gluing a lot of 4/4 stock.