The problem with Cape Verde is that it's just a bit too far away. Operating an A321 there would require a night stop. That massively increases costs. As some have already mentioned, TUI operate the Cape Verde with a night stop for crew on the 737 MAX. The Dreamliner is a little faster and can do it there and back in a day but crew duty is still tight.
If we look at Maderia yesterday for example, eight Jet2 flights were scheduled. All of them diverted due to the weather there. At least half of those were forced to night stop as the crews were running out of duty. Madieria is approximately 2-2.5 hours closer to home than Cape Verde.