Euro BB bearings are very small and crush easily.
With normal bmx this is not an issue, since the bearings are actually designed to take vertical loads (most of the force normal bmx gives bearings during normal use, i.e: not falling off)
however with flatland we put all sorts of strange angled forces on the bike daily - forces that bearings, handlebars and frames by their very nature are not designed to take.
Plus we fall off probably a bit more learning tricks.
So if you keep slamming your cranks/pedals into the ground looping out of tricks, or trying whoppers - those bearing will not last you very long.
I used to go through spanish BB's once every 2/3 months, however I have learnt to bail my tricks differently and save my bike from slamming on most tricks.