Price, simplicity. 8m mirror size would equal some of the largest telescopes currently on the ground. A lost of cost could be saved, if the whole teslescope cou

Price, simplicity. 8m mirror size would equal some of the largest telescopes currently on the ground. A lost of cost could be saved, if the whole teslescope could be completely assembled on ground. Later iterations could have larger mirrors, but just having a Hubble replacement with modern cameras would be a huge step, having a 4x larger mirror will be magnificient enough.