Lots of reasons.
The crane was located in an old growth Douglas-fir/western hemlock /western red cedar forest (about 500 years old, but small in stature for its age by PNW standards).
This type and age of old-growth is the most prevalent remaining in the PNW. The crane was within a Research Natural Area, part of a system of small reserves set up by the USFS across the country to do basic silvicultural research (how to grow commercial species).
The grant was funded by NSF to set up and run a facility for basic canopy research in multiple areas. Scientists with funding for scientific research then paid to use the crane and facilities. There was also companion research done on the ground, and a 16 ha plot with every tree tagged, mapped, and remeasured for growth and mortality; some of these were within reach of the crane. All research was done with minimal impact to the site; there was an existing gravel road that had the power buried under it, and was upgraded by laying down geotextile and gravel. I helped build plastic-wood boardwalks to access the area of the crane circle for work there such as on roots, forest floor nutrient cycling, and atmospheric ground level sampling.
Using cranes for canopy research is a world-wide effort; this was one of the main sites in the US, and ran from 1995 to 2112 -- probably a record for continuous use of a tower crane in one place. Before they were used, scientists either had to shoot branches out of trees or climb them and sample them. The crane allows studying limbs still attached to the trees, easily replicated among multiple canopy levels and trees within a single day, and in the case with this crane, with the option of plugging in equipment to power in the basket..
Some of the projects I helped with when I was there included measuring rates of photosynthesis in tree canopies between 100 and 215 ft. (the tallest Douglas-fir), the influence of hemlock dwarf mistletoe on canopy architecture and tree physiology (the last pic in the group), insect herbivory of needles, and the influence if birds on it by eating the insects, calculating leaf area and branch geometry, and carbon flux of the whole stand. This last one made some headlines when it was found that this "decrepit" stand was storing away net amounts of carbon each year.
The tower was left to provide a platform of continuous meteorological readings, but the jib and motors were removed last year.
I can post more pics f there is interest -- I have to scan film slides.
