Straight teeth have proper contacts with each other, which means less food is expected to get trapped between them. In adults, the most common type of decay is contact decay – that is, decay that starts between two teeth. So if the contacts between the teeth trap less food, we expect less decay. The main factor for healthy teeth, however, remains oral hygiene. If a patient can clean well between their teeth and remove all the plaque, they will not develop cavities. Straight teeth are easier to clean. Crooked teeth are harder to clean, but it can still be done.
There is a chance that a tooth may decay during orthodontic treatment, and this again depends on how well you clean your teeth with braces or aligners. The longer treatment lasts, the more likely it is that decay will develop. That is why the best treatment plan is the optimal one – the one that achieves the best result in the shortest time.
This answer is for general information. Your own case needs an examination by an orthodontist.