It's no wonder if the maps feel smaller; they *are*. Specifically the larger maps; until Standard size they're about the same size as Civ V, or even a little bigger. But once you get to Large and Huge, they're very much smaller than in Civ V.
I'm not sure where I originally got these numbers from; probably Reddit. You may distrust them if you want, but I see no reason for anyone to lie about this:
Civ V Large map: 104 x 64 = 6,656 tiles
Civ VI Large map: 96 x 60 = 5,760 tiles (15,6 % smaller)
Civ V Huge map: 128 x 80 = 10,240 tiles
Civ VI Huge map: 106 x 66 = 6,996 tiles (46,4 % smaller!

)
Why they did this is uncertain, but I suspect it had to do with fitting the game into their 'locked in' system requirements. If someone couldn't play properly on a Huge map, there might be too much complaints. Basically it's corporate suits triumphing over creative tinkerers yet again.
EDIT: Ofc custom map sizes can override these limits, thankfully. If you look in the 'Maps and Map Scripts' forum here at CFC, Gedemon has made a script for generating Giant and Ludicrous size maps already. Iirc, Giant is 180 x something, so it should be enough.

On his world map (that is the main thing about his mod), that size slowed down my game pretty fiercely though, so make sure your computer is up to scratch if you try it (I dare not even try to load a 'Ludicrous' sized map

).