A lot of it, too, had to do with what the state-of-the-art of electro/mechanical (internal) component quality was limited by in its production tolerances 40-50 years' ago as well.
I mean: a well-known example (in vintage rebuild circles) involves a small-signal gain, TO-92 transistor Hitachi made in the '70s and '80s called a "2SC458". EVERY AKAI reel deck made between (approx. 1972-1980) is full of them AND: THEY ARE NOISEY AS EVER with their terminals oxidized (now) practically like soot.
Replacing them, for instance, with a modern equivalent called a "2SC1845" having far better frequency headroom extension specs (in addition to: a re-capping done with, say, all Nichicon Muse aluminum electrolytics and small blocking/filtering caps of ruby or metal polyester)....WILL, SERIOUSLY, PUT THE DECK (even just a plain-Jane-ho-hum consumer Akai!) INTO A WHOLE NEW LEAGUE the manufacturer never could've imagined(!). After all, even though one's average decent three-head/three-motor 1970s Akai wasn't a Scully 280 or Ampex 102: it was STILL a $600 hunk of equipment at the time (during what would've been the midst of a decade-long recession).
I did such a "hot-rodd" to the back-up Akai GX-365D I'd once found at a flea market for $25. It's a 59lb. machine from 1971 and, as I knew my way around with a soldering iron: I felt there was nothing to lose (I later found NOS Nortronics heads to retrofit onto it and, scrapped the glass ones which always had the worst crosstalk of any brand). THAT really changed things.
Off of a sine wive generator: it was now able to record from 11Hz to 21Khz at 7 1/2. With the 15 capstan adapter (since it's a rare 4 speed model): it recorded 11Hz to 25Khz.