Fame
Grant writing is behind-the-scenes work. If you need to bask in the glow of the spotlight, you'll need to buy your own lamp. Trust us, the paparazzi won't be camped outside your house waiting to catch a photo of you, the glamorous grant writer.
There can be a certain amount of vicarious fame. Landing a significant grant gives credibility to the organization seeking funding. If Bill and Melinda Gates want to throw money at it, it must be important, right? As the winning proposal writer, this newfound fame is (partly) due to you. Granted, the public may never know that, but hey, at least you know you're awesome.