Most remuxes have commentary tracks passed through. Heck, good encoder groups like QxR, TAoE and many Internal’s retain them.
I’ll agree remuxes generally drop extra video files though you don’t strictly need an iso for those, just a full BD disc dump in folder form which are far more common than ISO’s though far less common than single file remuxes.
I don’t think LoTR 4K’s changed the extras and behind the scenes from 1080p either so finding disc folder dumps of the old HD releases should suffice for OP if that’s all they want.