People have been whacking off to nothing but still images or text for literally all of human history until the 20th century. I'm pretty sure it's just a matter of being accustomed to the "moving pictures" format that's the barrier, like Dessolos suggests. But still images can be plenty erotic, as can text without any images whatsoever. Marquis De Sade, Kama Sutra, Greek and Roman sculptures and even dishware, Egyptian papyrus with erotica, naughty pottery in Peru, the manual by Marcantonio Raimondi, Lolita, Jin Ping Mei,...
Trust me: it can be absolutely erotic without images, let alone animations.