We use AWS Lambda because I was recommended to use microservices, and I'm sure glad I did.
A batch request asking for 50+ transaction IDs can be authenticated and redirected in one microservice, which then calls 20-30 others to get the data on each transaction ID. Then it can be passed to another microservice to format & send back to the front end.
At any stage of the process we're able to understand to what each microservice 'sees', what it does, and what it spits out.
Microservices also allow us to be more secure by splitting off transaction data and user data services. One microservice creates an authentication key, another uses that to make a search, no one microservice knows who is searching what and their result.
Lambda in particular is awesome because it starts up in less than a second, costs nothing while not running, and allows us to skip the labor/specialised knowledge of running a server.