Serverless has two things that I really like about it:

1. Scale to zero, which allows me to do things like automatically deploy a full environment for each branch in a project, with a full infra, frontend, backend, database, etc.

2. Good integration with IaC tools, so that I can define my infra and my runners in a single language/tool, be it terraform/cdk or something else. Most "monolithic" setups split configuring the infra and what runs in it into two tools/steps (please let me know of ones that don't!).

But if I actually run a application for a long time with somewhat consistent load there are always cheaper, more performant and flexible solutions than a serverless setup.