Because nearly every other android tablet has 1GB of RAM - the Nexus 10 and Galaxy Note 10.1 being the only tabs with 2GB. The TF300 is intended as a mid/upper-mid range tablet, not to compete with those models (if anything, ASUS not putting 2GB in the TF700 is a bigger deal).
Warning... a slight thread jack here....
Holy smokes! I hadn't heard about the new Archos tablets and just noted they are releasing a quad-core, 2GB, IPS screen with dual speakers tabby for $199!
That's a pretty awesome price. I have the Archos G9 80 (which is a dual core 8" with a TFT screen and built-in GPS). The only thing I don't like about the G9 is the crappy screen angles. There's an awesome community for the G9 and Archos is still supporting it with updates. The G9 right now goes for $200 so I'm stunned that their next Gen release replacement for the G9 is the same cost for a much better CPU, GPU and screen. Thanks for noting that. Repped.