What do modern, current day CD Transports do that older CDP's with RCA digital out don't?

we got a new georgehifi here doing politburo manifesto paste jobs

the world doesn‘t want to be saved, it wants better sound. Telling people that what they are hearing is delusional just won‘t wash I‘m afraid, especially when they wanted or expected the shiny new player to sound worse..

Expectation bias has been dashed on many an occasion.

I'm with Jasonbourne on the expensive cd transports. If you look closely at the inside photos of the Jaysaudio and CDbox, the units both use what appears to me, a cheap plastic cd drive inside of an expensive aluminum milled chassis. I have an older Sony ES and a Yamaha that have far better built drive assemblies. 

A BIG YAY for Sony xa5400ES, it's internal dac and processing, no outboard DAC.

I went thru 2 two Onkyo's, 2 Oppos, 1 KLH, 1 Denon, 1 Yamaha, 2 Sonys until I found out about the Sony ES players and chose a lightly used xa5400.

It's not just the transport, or just the single or multiple dacs, it's the OEM's specific combo of all other technology: re-clocking, up-sampling, anti-jitter, error correction dsd out without conversion to pcm, that you hear, this Sony is the end of the line for me. If it dies, I find another without any hesitation or sideways glance. I was buying LP versions of favorite CD's. Not anymore, now it's re-discover all my existing CDs, buy 'new to me' used CD's as well as 'new to me' new or used LPs.

the transport, drawer could be made of granite or cardboard, once the disc is in play it has been lifted up, sandwiched between two spinners with no support other than the center, spun between 200 and 500 rpm. 

People buy replacement transports for the Sony ES players, IOW it's vintage transport is 'good enough' to produce superlative results.

Digital Out can be different that the player's RCA outs

i.e. some do not always send SACD's DSD out the digital, but convert DSD to PCM internally

also, if sending to external dac, what internal OEM processing may have already occurred in older players prior to digital out?  I have no idea, just wondering if ....

I have an older Sony ES and a Yamaha that have far better built drive assemblies.

and if you go even further back, you have the “mechanism that doesn‘t wear out“, the grandaddy of them all, an engineering masterpiece that still eclipses anything ever built for durability. Is everything built henceforth a marketing ploy?……maybe…….