Well, even though I haven't actually seen ST:B, I'll still give it a shot.
K7 (from Trouble with Tribbles) was a deep space assignment, and despite having 3 arms, could only dock two ships at a time. There isn't really a reason to make it all that spiffy as was just a resupply depo for ships going through the system- it would be like a truckstop on route 66.
And while DS-9 was, from the perspective of Star Fleet, a deep space assignment, it was a garrison post for Cardassians keeping watch on Bajor, total capacity for 7000 people. Cardassians aren't known for their creature comforts- the Enterprise D had about 1,000 people and had two holodecks, but DS9 only had their holosuites due to Quark knowing what people want. K7 was the truckstop, DS9 was a barracks.
So, then we get to Starbase Yorktown, which had, among other things, a shipyard and 3,000,000 people. It was not built as a layover or military checkpoint, but as a fully functioning flagcity for the Federation. You can bet that it would be built with the idea to sparkle and awe any who saw it to show how ideal Federation life was.
At this point, we don't even need to bring up that it is in a different timeline- it was built different with different technology as it served a fundamentally different purpose compared to K7 and DS9.