CORBA VS Webservices
Why WebServices took advantage over CORBA ?
Answer
I suspect everything started from the firewall issues: CORBA requests are binary, multiple random ports are required for the normal work so CORBA requests and responses used to be blocked by firewalls when these first appeared. HTTP and FTP also use phantom ports, but these protocols were in much more wider use so immediately was obvious that firewalls must be configured to allow them. As a result, developers cannot rely on possibility to have CORBA connection between the server and end user PC and need to use some more firewall friendly approach.
Firewalls appear much less an issue in communication between the specialized servers than can use separate networks, IP/MAC filtering, specialized firewalls and the like. I think CORBA, same as JDBC, are still used to communicate data between servers.
It may also be a factor that CORBA messages use aligned fields (to match boundary alignments as they are used in C/C++ data structures). Derived protocols (like Google Protocol buffers) do not send unnecessary bytes just for alignment. Hence they messages are compact and these protocols may be preferred when binary messages and fast pre-generated message parsers are desired. Protocol buffers that appear for me rather similar to CORBA by design (IDL-like compiler, stubs and servants, binary messages, language interoperability) is really far from decline, being internally used in many Google services.
While CORBA framework is complex, a "properly done" web service stack is also not exactly trivial, so I do not think that the complexity of the standard has been an issue. Similarly, while the original OMG specification documents may appear horrible, the similar SOAP/WDSL specifications are equally complex, probably it is difficult to document a standard in an easy to read way.
CORBA protocols are not proprietary, they have been implemented in Free software many times, including JacORB and also GNU/Classpath implementations (well, now OpenJDK is also Free).