This has come up numerous times on the mailing list and is well known. Here are 3 from a google search but I remember many more [1,2,3]

The problem we have that others do not is internationalisation.

Evidence shows just labelling it menu does wonders but this doesn't necessarily work in other languages.

I think there's lots of kudos to be had here if a designer wants to tackle this problem.

So maybe the real question is: is the reason this hasn't been tackled because it's a hard problem or we have more important things to do or something else?

[1] https://www.mail-archive.com/search?l=mobile-l@lists.wikimedia.org&q=subject:%22%5BWikimediaMobile%5D+Analysis+of+the+hamburger+icon%22&o=newest&f=1

[2]http://osdir.lowified.com/general/2013-11/msg26826.html
[3] http://mobile-l.wikimedia.narkive.com/NUkNZ4Xr/wikimediamobile-usability-of-the-hamburger-icon