The idea of replacing the boilers in an existing central energy plant can be daunting. This is very high capacity, very large, and very pricey equipment. The renovation can take a long time and require extensive modifications to the existing mechanical room. The logistics of getting the old equipment out and getting the new in is a full project by itself.
System design is a critical element of system efficiency. The hydronic heating system must be designed correctly to take full advantage of a high efficiency high turndown boiler. It makes sense that a high efficiency boiler will never perform at a high level in a system designed for an atmospheric boiler. The physics is just against performance.