Grove crane built the first tms 250 and tms 300's in 1973. Those two models were built virtually unchanged from 1973, until the mid/late 1990's. The model 30 winches the tms 300 used were supplied with some grove cranes until the mid 2000's.
They are a simple, good design, no need to reinvent the wheel every year. The computer systems installed on a lot of the new stuff, in 10 years is no longer made/supported, so you can have a machine you can't run.
Nobody want's to build a crane with a 20' outrigger span, because they get a lot better chart with a 24' span, and less counterweight. Never mind that most driveways are less than 24'. National finally heard enough complaints, but instead of 20' they give you a 1/2 outrigger chart (which doesn't help much- your tailswing is still wider). And they give you a option of longer jacks, because everyone whines they are a pain to set up in a crooked spot.
The market for dedicated truck carriers has gotten tougher also, because of emissions. Its easier to just have kenworth, pete, and freightliner deal with the constant new engine designs, and just build a crane that mounts on their truck, than make their own. The design costs have to be horrible, for no more units than they would sell, to build a truck crane today.
Pre 2000's day cab semi-tractors by me are at a premium, if in good shape. No one wants to deal with e-logs, or again, the emissions. t800 and w900's. 359 and 379's. 3406- N-14, 12.7 60 series. Even good r-series mack dumps will bring good money. Good simple designs. Older Road trucks can have sleepers pulled and become day cabs or dumps. Not with any of the new areo trucks- the used market for them is nothing- their only worth is in parts- engine trans and rears.
late-90's early 2000 ford 7.3 and dodge cummins trucks are also premium priced. The problem with most of them, is that they are getting to have so many miles on them, they are almost unrebuildable. Two ford's side by side- one with a 7.3 and one with a 6.4, but the 6.4 ten years newer, will be $8-10,000 difference, and not for the newer truck.
"The dirt is the same as it ever was, we just keep inventing more and more complicated ways to move it" - paraphrased from Scrub Puller- ( I miss reading his posts)