There is a huge opportunity building up and selling Amazon FBA businesses right now. Many more are being listed on mainstream marketplaces such as empireflippers.com (who recently wrote this excellent guide on the FBA business model) and there is even a dedicated FBA broker.
There is also a big risk with only having Amazon as your only sales channel and traffic source and many FBA businesses are looking to diversify through building their own shopify stores and funnels.
The issue with Amazon is that they own your customers. Sure you can follow up by messaging people who purchased your product through the platform but you can’t market to them and build you own list.
It’s a good idea to diversify traffic sources and build your own list. It doesn’t make sense to send traffic straight to your Amazon page as you can’t measure the effectiveness of your ad spend as obviously cannot put conversion tracking code on Amazon.
What you can do is create a marketing funnel that builds a customer list, increases your sales velocity on Amazon and generates product reviews on your listing. All of this increases the likelihood of your product being found by other people.