Have you heard that many of these contracts come with preselected tech stacks or have to integrate with legacy systems that violate the standard your contracts

Have you heard that many of these contracts come with preselected tech stacks or have to integrate with legacy systems that violate the standard your contracts have to adhere to? Your requirements will change every few quarters and those requirements may dictate a completely different tech stack? One lovely contract I worked on required C#, C++, and then Java. All within the span of 2 years. The actual project goals were so removed from the original stated goal that it would not have been even remotely recognized by the original project lead. That's good because the project lead changed three times.