Bitcoin regularly moves in tandem with SPX and this effect will continue to strengthen as more ETFs become available, and futures volume (on classic regulated exchanges) increases. These instruments are gateways that enable a much larger class of investors to come into Bitcoin cheaply, but it also means Bitcoin joins their portfolios and is treated similarly to other asset classes during market events. Uncorrelated, mass adoption: pick one.

During the massively undersubscribed 7 year note auction last month BTC absolutely tanked and recovered in perfect synchrony with SPX, TLT and gold.

During a recent deleveraging event (last month I believe), it was possible to observe BTC following an identical path to SPX for almost the entire day.