As I've been a part of the NYC improv community, I've found that a lot of the students taking part in improv are either actors or people who want to take acting. The remainder are a combination of people trying to meet new people and people trying to get over a fear. Admittedly, this is a huge generalization but for the purposes of this blog, it works.
On the one hand, you have acting teachers and agents recommending improv for actors to help with comedy or commercial work. On the other hand, you have improv teachers basically teaching people how to accept themselves and be comfortable with being themselves in front of other people.
In voiceover, you may do a million voices but when confronted with natural or conversational, you're more likely to just do your voice. In this aspect, Improv shines through. You're comfortable and your having fun. But, you need to know the basics of acting to get through it as well. Hitting certain words, being able to separate scripts into beats, using your body, those are all acting techniques.
So, unfortunately, the improviser and actor get closer and closer together to the point where most actors do improv and most improvisers have acted. The rare cases when they are successful in both is where you probably know the names of those famous people.
If you're looking to learn acting or get into voice over. Feel free to connect to my website Everything Voice Over.
Have a great day everyone!