The sound you get from listening to old recordings or "digitally remastered" is contingent upon the audio equipment you play back on. Back in the day Motown was known for their high fidelity sound, as they used a lot of custom made preamps and effects. Fast forward to the late 1980. Sub woofers became popular, and recording studios started to mix for the sub bass frequencies which didn't exist in most of the pre 80's music.
By the early 90s CD, and digital audio was becoming the standard. Thus audio equipment changed, and continues to evolve at a rapid pace.
Nevertheless, older stereo systems, and expensive audiophile system will reproduce the best sounds from the old recording the way it was intended to be heard. Modern, digital playback devices and cheaper digital audio playback systems will playback the analog recording to sound different.
And the reason for that is. Technology in the digital era operates at a wider frequency range, and has more headroom for volume than did the old analog recordings. Thus, modern recordings are mixed different that they did back in the 60s and 70s. Also, the playback devices enhance specific frequencies to make it sound clearer. And they can make instruments stand out, or up front.
The age of mp3 and compressed music. This also affects the quality of sound. Thus, manufacturers of consumer electronics, build their electronics to enhance the sound of the compressed music format. In addition, companies that manufacture speakers, headphones, and earbuds, also, enhance their products to boost bass frequencies, or specific vocal frequencies to make their product more appealing to the masses.
So there you have it. This is why old music may not sound as good as the new music. But with the right playback equipment, old music can sound good. In fact with good quality vintage stereo receivers, turntables, and speakers, you'll hear things in those old recordings that you just can't hear on the consumer grade digital playback devices.