Rather than explaining why you're leaving your current position, pivot around and explain why you're so interested/a great fit for the job you're interviewing for.
"Why are you leaving Soul Crusher & Associates?" As much as I've learned and grown as $currentRole, I've always hoped to be able to work as $interviewRole and can see myself contributing so much more at $newCorp because ...
"Why are you leaving Soul Crusher & Associates?" As much as I've learned and grown as $currentRole, I've always hoped to be able to work as $interviewRole and can see myself contributing so much more at $newCorp because ...