...Also, again it should be pointed out that we don't know how or whether transparent aluminum shatters. There's nothing to say that the display case isn't made of transparent aluminum.
In terms of physics, if it's transparent, then it's inherently brittle. Transparency is rigidity, down at the atomic level, and rigid structures shatter. If you make a display case or a drinking glass out of transparent aluminum, it might be very strong up till a certain point, at which it shatters - and 24th designers would rather make use of these qualities by manufacturing the display case and the glass so that they are at most as strong as their glass-made equivalents but much thinner and lighter. Perhaps there's no requirement for an unbreakable glass or display case, but it's always a good idea to have these things take up less of the "payload mass"...
That's how we make automobiles today, after all. Today's stainless steel is better than its 1950s equivalent, but today's cars rust out more quickly and are more vulnerable to getting dented because we have chosen to use the superior qualities of the material to make the cars lighter, not more durable or even equally durable.
Timo Saloniemi