I think there are a few factors. Most never really considered Ashlee a vocal talent. She was popular at that time, but she hadn't proved herself as a singer. Many know Beyonce has vocal talent, and is known for it. Secondly, Ashlee was caught in an embarrassing situation. If it had gone smoothly, I doubt as many people would've cared. If Beyonce's track had skipped and she just stood there awkwardly and then did a weird dance thing, she would be a meme already. Also, Ashlee was a douche about it and blamed everyone but herself. She threw a couple people under the bus, including her own band, and it made her come off pretty bad. Then, when she had her Orange Bowl (I think) performance to redeem herself, most people considered her performance terrible and that didn't help.