Largely because it's relevant to the notion that there's an alternate path to accruing the 563m credits required to buy all of the 529 cars in the game than grinding the same four races.
Most people should be able to get a silver in every time trial; that's 1m a week or 52m in a year. Everyone should be able to complete every weekly; that's very roughly 1.3m a week, or 67m a year. Everyone should be able to do 25 Daily Marathons a month; that averages out at about 1m a month, or 12m a year. Combined that's 23% of the total credits you need, just from those three things everyone should be able to do, which gives you just about four years to earn all the credits required without touching the grind races.
You can of course shave that down a lot too. If you have PS Plus you only need to complete a couple of races per GTWS season to get 1.5m credits. That's worth about 7m a year.
There's regular Six-Star tickets giving high-value cars in the Weekly Challenges and each one you get (remember, we're assuming you have no cars at all for the 563m spend; there is diminishing returns on this though and they'll eventually be worth a third of that in resale value) reduces your required credits by at least 500k. That'll happen about once every two months - and you get 500k/1M twice as often - and you're also getting about one a month from the 25 Daily Marathons (plus two other lower-value cars), as well as some cars from completing licences and missions at Bronze (obviously way more if you get gold, but we're not assuming that).
Additionally there's regular car giveaways (at GTWS events; averaging out at two usually high-value cars per live event) and your guessing skills should earn you about 1m from the eight opportunities to do so each year. And the 15m D-Type is available for free.
All in, you're probably looking at a little under three years, even as a normal player, to earn enough credits and cars as credits-in-kind, to accumulate them all without grinding. A good player can do it in a lot less.
Except Invitation cars, which are pure luck and still suck for that reason.
Yes; people want things faster so they have the options available for them or so that they don't miss out on something in a rotation. I've done a few Spa races myself, just to get the credits now while a car I need is in Legends.
However choosing to do so is not the same as "basically requires" - which was the original statement that is being repudiated.
The game economy - while still not exactly on-point - has come on quite a bit, but some still insist on treating it like it was in April 2022. It no longer "basically requires" grinding one or several of four specific races. You can do that, sure, but it's not basically required any more.