Indeed there is a reason. It can be described in just two words:
1) lazy
2) programmers

And yes, I am speaking from experience. I am a programmer myself and the way I see my fellow programmers waste resources pains me to no end. The algorithm runs too slowly or runs out of memory? Why bother investigating the cause, just give it a higher priority or allocate a bigger buffer!

Unfortunately I see this kind of attitude everywhere, its application in programming is that, one application out of many. Other examples: driving in the middle lane of an empty three-lane motorway... a group of three taking a table for 6 when smaller tables are available... buying a bigger pack of yoghurt in the full knowledge that you will never finish it and end up throwing it away - but it's only 10% dearer than the small pack, so what?... keeping the fridge door open while pouring the milk in your tea, because who cares, right?

It is this attitude that means that 1GB is not enough for a task that just a few years ago ran happily on 4MB, nothing else.