As others have mentioned the reason the tether is there is due to the limited resources (processing power, memory, and limitations on how fast your hard drive or solid state drive can load) the consoles have. Yes, they could put in an option to adjust the length but to be honest the tether is more likely then not already optimized. Stretching the tether further would require more memory and would put a much greater load on your consoles processor and storage media. If your console starts to run out of memory your game will crash, if it overloads the processor and/or storage media everything will start to run really sluggish. It'd take much, much longer to load bases or new terrain as you get closer to it assuming the game doesn't crash from the strain or worse yet, causes so much heat output so as to damage your console at which point you'd need to buy a new one. Long story short: Sorry, it can't be done. The tether is there to keep your console alive and healthy.