Well the main reason is that unless you make one up from a server PS, a 1400Watt power supply costs more than a 1400 Watt battery charger.
That is a lot of power and decent safe power supplies of this capacity that run off potentially lethal mains supplies are not a trivial item.The simple economics is that not everyone wants a built in mains supply and they would have to be certified for a range of different power systems.
When you get up into the 1000W class of LiPo charger it is a lot simpler to make a single item running off a low voltage supply which does not require all that hassle of mains certification in each country and let the local customer/3rd party vendors supply the mains -> DC solution.
Originally Posted by Daravon
Can someone please explain to me why all these fancy battery chargers do not come with internal, A/C power supplies and simply plug into the wall like any other piece of electronics gear is expected to do?