Why do some template parameters in conventional algorithms use rvalue references while others don't?

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There are a few reasons why some template parameters in conventional algorithms use rvalue references while others don't:

1. Efficiency: Rvalue references allow algorithms to efficiently move data instead of copying it. When dealing with large, complex data structures like containers, this can be a significant performance boost.

2. Flexibility: Rvalue references allow algorithms to accept a wider range of inputs. For example, an algorithm that takes an rvalue reference can accept both temporary objects and objects that have been explicitly moved via std::move.

3. Compatibility: Some algorithms are designed to work with older code that may not support rvalue references. In these cases, non-rvalue reference parameters are used to maintain backwards compatibility.

Overall, the choice to use rvalue references or not depends on the specific requirements and constraints of each algorithm. In general, however, rvalue references are useful for improving performance and increasing flexibility in modern C++ code.