Bitcoin prices have plummeted and people are pulling out
Nope. This suggests that demand for GPU mining is going down. It has nothing to do with Bitcoin, which can't be mined with GPUs anymore. The altcoin market is suffering alongside the demand for their mining equipment.
Mining is declining
For altcoins, you're probably right. Bitcoin mining is as popular as ever though. In fact, the
hashrate has recently recorded all all time high.