Automation malfunctions caused by the SmartThings infrastructure (at the time) were attributed to the predecessor of Rule Machine. That led Rule Machine to being pulled on that platform, and the desire to create a cloud-independent automation system.
SmartThings being purchased by Samsung had no bearing on that latter decision. OTOH, SmartThings' recent decision to abandon Groovy was driven by their acquisition.
Here's @bravenel's summary on why he founded Hubitat, along with its early history.