Expensive and probably just not worth the benefits compared to more conventional alloys and you can also make carbon fiber or titanium bikes. Magnesium-alloy bikes are also quite rare and beryllium even more so.
The cycling industry is quite interesting. Their advertising is trying to give the impression of a high tech industry with plenty of R&D and every year you read about the most recent "breakthrough" (aero/weight/compliance). However even the largest bike manufacturers have maximum a a few tens of engineers who develop the bikes and components across the whole range. That already tells you how much R&D they can do realistically.
arrwl --> steel