Think of the distinction between "over the board" and "online" as kind of like the distinction between "NBA game" and "pickup game". Even that might be understating it. The levels of importance are radically different.
Also, think about how much harder it would be to cheat over the board. You might use hidden devices, accomplices, secret signals--compare that to an online game where all you need to do is switch over to another tab to check the engine. Cheating OTB requires a significantly greater degree of forethought, planning, and commitment--a persistent and repeated willingness to cheat that is way less acceptable than an online player getting tilted and looking at an engine. Still cheating, yeah--but at least it's not premeditated.
Also, think about how much harder it would be to cheat over the board. You might use hidden devices, accomplices, secret signals--compare that to an online game where all you need to do is switch over to another tab to check the engine. Cheating OTB requires a significantly greater degree of forethought, planning, and commitment--a persistent and repeated willingness to cheat that is way less acceptable than an online player getting tilted and looking at an engine. Still cheating, yeah--but at least it's not premeditated.