I can't tell who's being deliberately stupid or actually surprised anymore, so instead of talking in circles let's clear up everything:
What is Gran Turismo Sport?
It is a game that is focused on online racing, a major departure from the series. Specifically it is FIA licensed, meaning it is one of the only racers that can be used to gain a FIA license.
The game contains "Sport Mode" where you rise up in ranks as you play online with others, as well as hundreds of smaller events that teaches you basic driving skills (Driving School), some of the nuances of each track (Circuit Experience), and pit you in specific situations (Missions).
You can also play an Arcade mode that let's you play freely on all the tracks and cars in the game, and take photos in Scape mode.
What Online/Offline Functionality is There?
Online, PS Plus Sub: All features are playable.
Online, no PS Plus Sub: All features except for Sports mode (online racing) are available.
Offline: Only Arcade mode is available. No progression is saved in this mode.
Why are saves cloud only?
To prevent data tampering and online cheating, and for the game to be officially certified by the FIA.
Why isn't there an offline save option?
The entire point of the game is to ready you for online racing. The work involved for separating components of the game to save offline probably wasn't worth it, because all progression goes towards matching you up with the proper opponents online.
So I can't save single player progress without online?!
There is a single player component, but it's nothing like the other GT games in terms of progression. You should not buy this game if your only focus is to play the single player content. That is not what this game is built or designed for.
Should I play this game if I don't want to play online?
The entire focus of this game is an online racing series. To put it another way: you can buy Battlefield for the single player, but...that's not the best idea. This is an online focused game.
They should have made this obvious from the get go!
They did. They mentioned it from the original announcement all the way to this crazy
"burn the series to the ground" hype trailer, GT Sport was always all about online racing.
They should put the online requirements on the back of the box!
They put it on the front of the box.
What happens in four to eight years when the servers get shut off?
The same thing that happens to all online-focused games: they become unplayable.
Are you seriously ok with an online focused game forcing you to be online at all times?
That's a stupid question.
What happens if the servers go down due to maintenance?
That's a legit question, and I'm sure we'll find out when it happens. Polyphony added more user support to their servers due to the overload when the beta/demo hit, so we'll have to wait and see.
And what about the lootbox and microtransactions?
They have already confirmed
no lootboxes or microtransactions will ever appear in this game.