I asked why they should, you haven't answered that.
But of course that's a rethorical question: every company sets the price for their product however they want. As long as they aren't breaking any law, there is nothing wrong about their pricing, sales or marketting policies. You are free to make you own assessment regarding the product's quality with relation to its price, like every consumer should, but to claim that Frontier aren't supposed to be able to sell whatever additional content for their product for whatever additional price is ridiculous. I can't remember Frontier advertising free of charge paintjobs, so who cares if this is a "full" price or F2P game? If you want the paintjobs, and Frontier don't want to give them away for free, you buy them, you grind them, or you make do without them. There's no should involved, it's a simple price/value proposition.
Where did you see in post that I was talking about legalities? I did not say that I am gonna sue them for false advertising either, so I do not really see the point of bringing up these irrelevant points to the discussion. I did answer ... they should because that is how a good game should be. No predatory monetisation or practices should be in any game and no game dev should force players (directly or indirectly) to pay insane amount money for a skin. Simply because the law does not prohibit something, does not make it right or wrong. Once again, I am not debating whether I am free to make choices or the legality of what they doing so do not sway the conversation this way.