Why are cots so big?

Had a look round the baby expo yesterday, as I am a bit clueless and thought at least would give me a few things to think about, one thing struck me why are cots all so big? It seems like they are big enough to fit a four your old in, and surely the child would want to be out of the cot by the time they are anywhere near that age. We live in not that big two bed flat and it seemed that most of the cots I saw yesterday would take up most of the second bedroom - are there any smaller cots about? (Apparently I refused to sleep in my cot at about 14 months and insisted on sleeping in my own normal bed instead)

a lot of cots now convert to junior beds as well

i'm guessing they are the size they are because a lot of "babies" don't lay still all night - they move around, and don't want to be hitting against the sides of the cot as they do... i think they're a pretty standard size, except for boori cots (which are bigger)