I don't actually know the reason. I'll see if I can find out and whether it's appropriate to share. It's possible that it's a redundancy thing (have multiple providers so we stay up if one goes down), a performance thing, or it could be a features thing. I don't know.
I will note that what Akamai is trying to do: serve static content extremely quickly from locations close to all customers, is a bit different from what the typical AWS services and AWS region are trying to do. Akamai probably wants to cache identical content all over the world, in boxes that I would expect to be present within the network of many different ISPs (just like Netflix does to serve its video [1]).
In Oct 2019, CloudFront announced that they had 200 different points of presence (POPS) around the globe [2]. I don't know exactly how to compare Akamai to CloudFront, but Akamai claims to have POPs in over 130 countries and in 1,700 networks [3]. Akamai was founded only four years after Amazon and has been focused on content distribution since then. Just like a company can't snap their fingers and have Amazon's retail logistics presence, AWS can't snap its fingers and have CloudFront POPs in every country/network/ISP where Amazon Retail needs good performance. The answer may be that they're still catching up.
I'm completely I'm speculating though, and don't have any knowledge about this beyond the public research that I linked to.
[1] https://openconnect.netflix.com/en/
[2] https://aws.amazon.com/blogs/aws/200-amazon-cloudfront-point...
[3] https://www.akamai.com/us/en/resources/visualizing-akamai/me...
