Eclipse CDT provides a group of preferences that affect how the CDT editor handles big C/C++ files. These preferences are found in the Preferences dialog at C/C++ - Editor - Scalability.
Basically, when a C/C++ file is bigger than a specified number of lines, CDT enters a "scalability mode". It then turns off some editor features to retain acceptable performance when editing large files. By default, the file size limit for entering scalability mode is set as low as 5000 lines of code. Files generated by Model RealTime often exceed this limit. If you have a powerful enough machine, there is no reason not to raise this limit to get benefit from all the CDT editor features even with large C/C++ files.