Besides of the popularity of micro-services and that I personally enjoyed developing MS in the past, I think it's a tool to be used carefully and only after a well done technical analysis. The advantages of performance and horizontal escalation that a MS architecture offers, can be easily.
Personally I've seen projects being migrated to a MS architecture only because it's "cool" and not supported by an exhaustive analysis. This maybe it's will not lead to a performance problem, not make too much differences in the operational cost, but then, why making all the effort and taking the risk?
Besides of the popularity of MS and that I personally enjoyed learning and developing MS in the past, I think it's a tool to be used carefully and only after a well done technical analysis that justifies the implementation. Personally I've seen projects being migrated to a MS architecture only because it's "cool" and not supported by a well sustained technical analysis.
MS offers several benefits, such as the capacity to horizontally escalate a small piece of your application, instead of the entire app, separate the source code into different repositories, allowing to introduce different frameworks and languages if necessary, makes easier to writing unit tests, and to have separated deployment pipelines, which is of course great for large applications that can carry on several, non related projects and deliveries, by allowing the teams to split into several squads in an easier way. however, the advantages of maintainability and performance, can be easily waisted by over-engineering projects with unnecessary components, increasing the network latency (communication between services). also, must be consider DevOps increasing costs.
On the other side, a monolith application can offer several benefits over MS, specially when working with small teams with and reduced resources. A development are much easier to implement, and, making easier deployments, reducing network costs, among others. From a developer perspective, having your entire source code in the same repository offers several benefits as well. Regarding to maintainability, a monolith can be harder to maintain, specially when it starts to grow, and it will require probably a higher effort in terms of writing good quality code and code patterns implementation.