I've seen some of those applications. It might be easier & faster to start with a schema-less json database, but I saw some serious maintenance issues with applications like that:

* Using the stored data outside the use cases imagined by the original developer is harder than it should be. (Oh you want a customer dashboard with this and this data correlated, ..)

* "Migrations" can be rather error-prone if developers don't pay attention. (It was stored as a string first, and now it's an integer, now how do we query that). Just because there's no database schema, doesn't mean there's no schema.

* It's hard to see what's actually in a json table/collection. You'd need to browse the code, see how it's used, and then browse through the available data.