We don't ban people simply for voicing their opinions (though there was an existing thread on the topic he wanted to discuss, as was pointed out to him already).
CarBastard sums up the entire discussion pretty nicely; in the days of GT4 (ie. Standard Models), this proliferation allowed PD to easily include the entire model line instead of just one car. An Evo GSR and an RS were only a few minute visual changes apart, the biggest and most obvious being the smaller steelies of the RS. Oh, and it's lighter. It gave us options; the RS exists as the cheapest entry point for the "real" Evo, and a lot of teams would use it as the basis for a rally car, so equipping it with cheap, crappy rims made sense, since they'd just be swapped out. Of course, since we can't change tire width or rim size in GT, the effect is somewhat lost...
Nowadays, with the interiors of Premiums, this sort of approach is still possible (and still quicker to produce two trim levels of Car A versus the time to make Car A and Car B), but the decision has to be balanced between providing a varied car line-up. It's a balancing act, essentially.
Of course, then there's the actual duplicates; the made-up Lexii, for example, or the myriad Miatas that are all identical to one another bar a colour option or which side the wheel is on. That is something I really hope we're rid of with the next game 👍