Maybe because they had a full orchestra with actual musicians playing together at the same time in an actual acoustic space... ditto for the early rock recordings... now music is laid down a track at a time with very little interplay. IMO, the music was just better. In the day, we took it for granted... now we look back in awe.
Modern recordings have been processed so they fill all the frequencies and compressed so they are at nearly maximum volume at all times. Further, they have been quantized or played against a click so a lot of the feel has been eliminated. Older recordings had holes, fluid tempos, and dynamics that draw you into the musical space. Just MHO.