Pressing a button is apparently a BETTER way to activate a light -- which is probably why MOST watch companies use buttons!
A "momentary switch" is simple, inexpensive to produce, and probably less prone to failure than any mechanism that is going to recognize a "double tap," which will surely be more complicated. (Even the fairly simple microswitch for the "auto EL" had more reported problems than the basic "light button.")
Big companies generally like "simple," which is also usually "inexpensive" -- maximizing profits is part of how they got to be big companies in the first place.
Maybe you should just BUILD your own watch, instead of trying to second-guess entire teams of Casio engineers several times a day. :-d
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