The defi could be the side reason but there are some reasons why binance was growing so hard even when another did small increase.
1. Binance chain is having very small fees
2. There are lots of utility usage of binance coin
3. Binance was also regularly doing burn
4 You can earn so many advantage from the various platforms use BNB like cake and many more. That's why BNB was getting hyped due to the these reasons.