You only need a distributed OLTP database once you scale e.g. you have customers all over the world or if you are in a space the requires it like gaming, fin/tech, gambling, etc.... I think the reason they are gaining popularity is because the barrier to entry has been lowered both technically and financially. CockroachDB and Yugabyte for example are open sourced have a good entry point for their managed solutions and are mostly compatible with PostgreSQL. The large cloud providers are also offering solutions that let you incrementally scale to a distributed DB as you need it.
I have worked in Fintech where we needed a distributed database, as startup where we grew to the point of needing one, and am hoping to grow what I am currently working on to the point of needing one but we are not there yet.