XRP Base Reserve


So XRP has something called Base Reserve. You need minimum 20XRP in the address, and that 20XRP will be locked.

Can anyone explain to me what’s the reason behind it? Because if everyone has locked 20XRP it just mean you don’t have it.

Additionaly there is something called Owner reserve (5XRP per object). Does that mean in practice you actually need min 25XRP in the address? And is that 5XRP also ‘locked’?