But there is no deployment delay for the dependencies, so why can't calling the dependencies live in the cloud work?

Are you saying you need an environment to test in that is 100% disconnected from the internet? Given the interconnectedness of APIs in 2019, that seems like making things harder than necessary.

For at-work projects, I don't want to/don't have the bandwidth to be responsible for developers not cleaning up after themselves or exploding DynamoDB with a million write requests or whatever. My team has not yet demonstrated that they can self-manage cloud dependencies and I don't have time to do it for them.

For personal projects, having to futz with Pulumi--and, I should note, Pulumi is the one I like--just to write some code on top of a web server just really sucks. Iterating on a heckin' cloud template just to be able to write some code sucks. Waiting (and as somebody who works on devops projects primarily at work, I am very familiar with how long one waits) destroys motivation to work on anything, both at the start of a session and in the middle--like, blowing away all those dependencies when I need to reset takes way longer than `docker-compose down && docker-compose up`. I am also incredibly cheap for personal projects, because I cannot rationalize spending money on something I'm not certain I'm going to ship, and so I can't adequately ensure that AWS is not going to start dinging my credit card for resources.