I would say the relationship is this one:

First, Ethereum was found to be the perfect Ponzi scheme platform by dubious “ICO“ initiators.

Then, early investors made a huge bunch of money on these ICOs.

Then the price skyrocketed, as more people wanted some of that easy ICO money.

This in turn made the mixing services insanely popular, as all of those ICOs had to cash out, and knowing that their business was of dubious nature, many decided to obfuscate the target addresses of their ether via mixers to protect either OTC buyers or their personal accounts on exchanges from being linked with the ICO addresses.