On the other hand, I don't know what other way there could be to get a car in a racing game than racing and do tasks. If a car could be bought from the dealership straight away, the game would become boring even quicker, because getting money in this game and the price of cars is also a joke.
There's always room for a compromise option though - if you want a new car the moment it's available, win it with seasonal tasks. If you don't want to do that, or haven't bought the game yet, or don't have the skill to complete the tasks yet, there's nothing to stop them adding a fallback option later down the line to make that car more widely available, e.g. after two months it's added to the Autoshow for normal purchase.
The Crew: Wild Run did this to more of an extreme, where the top few thousand players on each platform could win the new cars a few months before they were widely available, and in fact Playground themselves started experimenting with something like this with the Backstage Pass system in FH4, where later seasonals awarded tokens that could be traded for certain previous prize cars.
The other side of this point also comes up frequently too, which is that all of these dozens of cars being added are generally unavailable long-term. I played FH3 between 4 and 5, and it was a really unenjoyable experience to play a racing game where about 30% of the car list was made up of content that was included in the price but I wasn't allowed to use because I bought the game too late. It's not even as if they were on the Auction House either, as the players who had won them originally had generally either kept them, sold them a long time ago, or quit playing for FH4.
I can only see it purely as a player retention tactic - play it now or miss out, and if you missed out or want a second one you need to keep playing until it's a prize again. It's in their favour, not ours.