I'm actually curious to see what 100 cars you have.
Anyway, that's your take on the cars you own. Someone that has the same 100 cars, and wants to keep them anyway, won't sell them, if they don't sell them, they don't earn money, if they don't earn that money, then their problem remains - low income of credits.
A huge percentage of cars in the game won't have their value go up either, specially if the player uses them. If the player modifies them, do they lose money? Do they gain? Having the cars as original as possible is one of the things that makes their value go up, so in the game, the more you spend on it, the less it's worth, right?
I don't get why would they complicate things. The game would revolve around buying and selling the same car right away, over and over again. Pretty much that would create a "meta", where there would be one car on the new car dealerships, that could be bought any time, and sold for a profit. This would also make racing worthless, because this new method would be the most effective way to make money.
They should add the ability for players to sell their cars, but to keep things somewhat balanced, it should be a given that the car will depreciate.
You make some good points. This complexity could in fact be why they decided to remove the car selling mechanic from the game (I believe selling was included in some of the pre-launch promotional blurb - it's detailed elsewhere on this forum).
Since you ask, the cars I have that are worth a few credits, and which I'd be willing to part with, are:
Toyota 86 Gr. B Rally Car (prize) 450,000
Toyota Supra Race Car (prize) 350,000
Lexus RC F GT3 prototype '16 (prize) 450,000
Ford GT '06 (prize) 460,000
Porsche Carrera RS CS (993) (bought second hand) circa 421,000
Ford Focus Gr.B Rally Car (prize) 450,000
Peugeot 205 Turbo 16 Evolution 2 ' 86 (prize) not sure how much it's worth
Porsche 917 Living Legend (came with the game) 1,000,000
Mazda RX-Vision GT3 Concept Stealth Model (came with the game) 450,000
Supra GT500 '97 (came with the game) 900,000
McLaren P1 GTR '16 (roulette ticket prize) 3,600,000
Porsche Carrera (prize for completing cafe menus) 2,300,000
Audi Sport quattro S1 Pikes Peak '87 (cafe menu prize - I think!) not sure how much this is worth - gotta be a lot though, right?
Ford Mark IV Race Car '67 (bought with every credit I had earned up to that point - and definitely not with it) 4,600,000
Those 14 are worth about 15.4m credits (more with the 205 and quattro). I figure I could scrape up a little more from some of the remaining 86. Most of what came with beating the Cafe Menu in fact.
I figure I could have flogged this lot, grinded out a few more credits, and kept some of my favourite vehicles. I'd then have the McLaren F1 based on a roulette spin prize, some cars than came with the game, and a load of cars I didn't ask for from the Cafe Menu.