If you need to hire someone to manage stuff you have to build or do yourself because DO doesn't support a solution yet, then that's something you could have spent on AWS. Do you really have spare devops talent just waiting around?
For example - SQS is pretty good and reliable - but you could use something like a rabbitmq droplet https://marketplace.digitalocean.com/apps/rabbitmq
How much traffic can that droplet handle? What happens if it fails? How is the droplet maintained and patched?
Or I could just call boto3 sqsqueue and be done with it... are queue's really the top cost of infra? Probably not - your top cost is probably database.
People probably build up a solution using AWS tech - and see where things suck. Then they move off those bottlenecks or cost tent-poles. If there are none - then stuff is left as is.