Dash on the other hand was sold off with the price kept stable at $7-8....why is this?
I wouldn't quite say they "rode it":
Examples: May 19th to June 12th (BTC rally started on May 26th)
Litecoin: 0.087 --> 0.008 (9% loss)
Ethereum: 0.033 --> 0.022 (33% loss)
Ripple: 1330 sats --> 901 (32% loss)
Basically, any currency that had recently "rallied off its base" just prior to Bitcoin lifting off got stung and the more they had rallied the more of a hit it took. Thats because the market is far more liquid close to an established base than it is at the top of a rally.
If we're generous we could maybe consider Dash 'established base' to be around 0.09 by now so from April it had rallied nearly 100% off it and therefore was simply much more exposed to a potential capital drain from a bitcoin rally than say the Litecoin market which was on the deck and highly liquid, or Ripple which had been falling for months or even Ethereum which was had just suffered a massive 60% consolidation loss in the couple of months prior to the BTC rally.