But fault tolerant workflow engine is not trivial thing, it may cost you many engineer hours to build, monitor and maintain it, so outsourcing it to someone else is totally viable solution.
The complexity and risk of migrating cloud providers eclipses whatever problem you assign to "fault tolerant workflow engines".
Any mention of AWS Step Functions makes absolutely no sense at all and reads at best like a non-sequitur.
If you get a good deal from one cloud provider, you can get started quickly.
It's useful even for individuals such as students who get free credits from these providers: create a cluster and you're up and running in no time.
Our rationale was that we didn't wanted to be tied to one cloud provider.
It’s like those stackoverflow answers that tell the user to stop using PHP and rewrite it in Python or something.
AWS Step Functions is a proprietary service provided exclusively by AWS, which reacts to events from AWS services and calls AWS Lambdas.
Unless you're already neck-deep in AWS, and are already comfortable paying through the nose for trivial things you can run yourself for free, it's hardly appropriate to even bring up AWS Step Functions as a valid alternative. For instance, Shopify's articles explicitly mention they are running their services in Google Cloud. Would it be appropriate to tell them to just migrate their whole services to AWS just because you like AWS Step Functions?