Why do turntables sound different?

In my opinion, there is a certain "musicality" that's missing in many direct drives. Inner detail, densely woven layered imagery, finesse etc. I would call them macro machines as they get a lot of the big things right, but miss out on the subtleties that make an exceptional table. One reason for this is they are NOT necessarily more speed stable than belt drives. My tables in particular often produce less wow flutter and drift. Coupling a motor to the platter, in my estimation is a compromised design. Modifying them and adding a good match may produce a better result, and I have not heard the modded tables, and of course variables like the room matter too.  Also, achieving the lowest possible w&f does NOT automatically make for a good sound. Other design criteria are just as important. 
Just my opinion

@anvil_turntables I have ordered a new bearing for my Technics, I took your suggestion and went for the sapphire-ceramic bearing.  This will be my last upgrade.  The next upgrade will be a new turntable of some kind.

If direct drive was obviously the best design approach not many turntable makers would stubbornly continue with the belt drive. Clearly, the situation is much more complex.
Ralph, though you express your own opinion, I think that you misinform some people. You did say that there were many tables that you had not heard. Why would you choose the Technics before auditioning all of the top tables? And tonearms. And cartridges.
I don't have an expertise to voice my opinion and I would certainly not rush when choosing one or another.
Intuitively, that's what I would expect from great belt drive design - quietness and sophistication. I don't need it for jazzrock but I do for the rest I care to listen to.

I would think that would make for a noticeable improvement. Also, don't misunderstand, as I think the Technics are excellent and great value too. I just think this whole w&f measurement thing is way overblown.  Maybe I am biased as I had some woeful experiences with direct drive Denons from the 70s and 80s that were a hollowed out grey sounding mess. 

Interesting thread. We all know table/arm combo's will sound different. I liken it to global climate change. We all know its going on but it is difficult if not impossible to distinctly say why. There are a lot of factors. I tend to like the high mass tables with air bearings in both the platter and arm as i "think" this helps isolate or protect against sound effects from non-groove sources. How much is caused by what mechanism but every link along the chain from the source (ie groove) to the speaker impacts. Even the wire choice on a moving coil is touted as having an impact on the sound. I tend to agree with the crux of many of the responses in that vibrations caused by a variety of sources will impact the sound. I know that bearing induced sound from my old Michell occurred and changed as i tried different bearing types and oil types. Even the air bearing system will have a faint sound, though much less than any other table i have heard, as i rotate the platter as even with these there still is a centering pin that does provide some contact from platter to the table base. I do also agree in keeping the table if possible in a separate room from the speakers. is this a huge impact, not sure, but i do it primarily to keep my electronics in a more controlled environment. 
Obviously these are just my opinions and not based on scientific measurement but rather from 40 years in the hobby with many different tables