I don't buy the whole "Studio Display is an almost-iMac thing" - lots of "analysts" were trying to make excuses for predicting an iMac release.
The fans are likely needed to keep the super-bright LCD panel and hefty power supply (enough to run the display
and provide 96W via Thunderbolt to charge Macbooks) cool - if you look at the
teardown the two fans are closer to the power supply boards than the logic board. An A13 phone chip won't need much cooling but an M-series processor, especially a Pro or Max (if they were going to offer an iMac range) still do - if Apple had any ideas about making an iMac they'd have had a fan over - or close & heatpiped to - the processor.
Likewise, people are probably reading too much into the "its got an iPhone running iOS in it" thing - a high end display like this needs a reasonably powerful controller, RAM, audio chip etc. so why would Apple use a third-party microcontroller and operating system when they've got a perfectly good in-house solution in the A13 and the iOS kernel - even if its slight overkill, they get it at 'mates rates', their developers know it inside out, the audio and webcam drivers probably reused iOS code... it probably
saved money.
If you look at the teardown for the LG Ultrafine 5k its got a cooling fan. It also has a 32-bit microcontroller, RAM and an audio IC... all of which could be replaced by an A-series SOC.
I think what made the Studio Display
expensive was turning it into a docking station for Macbooks while not relying on an external power brick
and keeping it so thin (its a
lot thinner than the 5k iMac was, although that was cleverly designed to hide its beer gut).