The root cause is that some manufacturers’ locomotives / decoders are not fully DCC compliant. Instead they use in house proprietary systems which require you to use only equipment supplied by them. Note the exact wording used below
LGB MTS and NMRA DCC Standards?
The LGB Multi-Train System is based on the principles of the NMRA "DCC" standard. However, the LGB Multi-Train System goes further than the standard to offer additional features, including full compatibility with the digital sound systems found in LGB locomotives and improved operation on outdoor layouts.
The LGB Multi-Train System also offers compatibility with NMRA-style "parallel" function commands. For more information, see Knowledge Database FAQ 1219.
Hint: Please note that we cannot offer assistance for users of third-party components.