I just checked their current BTC withdraw fee and found it's 0.001BTC (about $16.9). I'm sure the fee was 0.0005BTC or lower few months ago. It's unlikely they perform consolidation with such high fees, so your speculation could be right.
Yesterday, their withdrawal fees are much lower:
- 0.0005 BTC for Bitcoin Legacy
- 0.00025 BTC for Bitcoin Segwit
It means they increased withdrawal fees to two times (Legacy) and four times (Segwit) after spamming the mempool (assume it's actually Binance spam, not from others).