I welded for 15 years without burning a 6010. In boilers and nukes we NEVER used them. It was always GTAW/SMAW root/fill & cap. Sometime GTAW all the way. In commercial buildings (hospitals, colleges, high schools, barracks, prisons, etc) we use 6010 uphill all the time on mechanical piping (HHW,CHW,Steam and condensate) Sometimes RT/UT is required and 6010 uphill and 7018 fill/cap uphill is the norm. If the acceptance criteria is more stringent than the standard ASME B31.1 that commercial building often fall under I will use GTAW for the root/hot pass and 7018 it out.
You could weld it d/h with low/hy if you submit a qualified welding procedure and it is approved by the PE.
I have seen CBI weld the containment wall of the reactor building (1/2"thk) downhill with low/hy. in the early 80's. It can be done.
I think the pipeliners use 6010/7010 d/h for speed. They use high amperage and travel speed to complete welds faster. There may be some mechanical and metallurgical reasons also.
I think heavy wall is welded uphill most of the time. I am not a pipeline welder so I don't know if they use any HW pipe.
We have welded HW 360 uphill/downhill using machines.
As JTMcC stated "it's a big and broad welding world out there." I thought I knew a little bit about welding until I joined this forum.
One reason low hydrogen is welded uphill on structural is the deposition rate. You can carry more metal uphill with moderate heat input.