In the beginning, SqlWorkload used to read trace files using an API that works only in x86. While WorkloadTools can work in x86, using x64 builds is highly recommended, due to the possible high memory usage when capturing intensive workloads. Using a x86 API would have excluded the functionality from the x64 builds, hence using an external tool to convert trace files seems much more appropriate.
Now ConvertWorkload itself uses LocalDB to read trace and XE data, so it is not unreasonable to expect the same from SqlWorkload
In the beginning, SqlWorkload used to read trace files using an API that works only in x86. While WorkloadTools can work in x86, using x64 builds is highly recommended, due to the possible high memory usage when capturing intensive workloads. Using a x86 API would have excluded the functionality from the x64 builds, hence using an external tool to convert trace files seems much more appropriate.
Now ConvertWorkload itself uses LocalDB to read trace and XE data, so it is not unreasonable to expect the same from SqlWorkload