Because they operate at a low level of abstraction, they are tedious for a programmer to work with. Further, a typical RPC may require 24 distinct steps, several calls across a network, and much more processing power than a local procedure call. They don't scale well to a wide area network. Unlike other middleware, RPCs are not generally sold as standalone packages. Atomicity means that a transaction must execute either completely or not at all, leaving no partial results.
Consistency means that the transaction moves the database from one consistent state to another.
Isolation means that each transaction is isolated from the intermediate results that may be generated by others running concurrently. Durability means that once a transaction is complete, results will not be lost because of a system or storage failure. Still important, CICS runs on a wide variety of platforms. TP monitors may have a client component, but they do most of their work on the application server, connecting to multiple database servers and performing load balancing as needed. Like RPCs, TP monitors have traditionally been synchronous, which makes them suitable where data integrity is of prime importance, but not so useful for real-time data feeds.