They do because the more you buy, the less noticeable the increase is. At my level, the KP cost increases by 0.0063% so that's a very negligible increase comparing to increases for coins from residences, visits. Just increase in coins from visits from one MH upgrade is 4.76% and that's 758 KPs before it starts getting tiny bit more expensive again. We're playing with pennies.
Whatever you want to call it, it's a part of the game. It's another thing to analyse and decide which way to go. If the game was easy, it would be very boring.
The fact it becomes less noticable does NOT mean it gets cheaper. It means the percentage changes, which is something completely different.
If gas goes up from $3.50 to $3.60, then from $3.60 to $3.62 it does not mean the gas is getting cheaper because the increase is less. Not even if your wages were going up with the same amount in percentages. The fact you don't notice it as much has nothing to do with whether something actually goes up or down.
And I know it's part of the game, thank you very much. Doesn't mean it is not screwed. In fact, it is one of the reasons there are so many cross-tier trades. The increase in output for T3 factories has been far outpacing the increase in price for KPs. For both ranking points and buying KPs it is far more profitable to have more T3 factories than others.
If I want to buy an extra KP, I can pay 79.320 T1, or 41.080 T2, or 30.070 T3.
But the output of the factories is about the same. And the amount the next KP increases by is larger for T1 than T2 or T3,
It would be 79.360 vs 41.100 vs 30.080. Sure, doesn't seem to make a lot of difference, but it will add up over time....just look at the difference I have to pay. I could buy a crapload of extra KPs with T3 goods before I even get close to paying as much T3 goods as T1 goods
The system was designed to be ok when there was a big difference in the output...as in back when you couldn't upgrade T3 factories as far as T1 factories. Since so much in the game has changed, this probably needs to be looked at as well. The overhaul in the trading system helped bring down the ridiculous amount of cross-tier trades, but it didn't solve the other issues.
Saying it is part of the game is no argument at all; the game has evolved quite a bit, so there is no reason to just accept everything.
That all being said; for me it's not an issue in whether I can afford it. I can. Not all players can.
My issue is I am being forced to buy 100+ KPs at a moment where I basically have no use for them. If it is a few, all fine and dandy. When it is about large amounts it is not, it is an annoyance.
Since there have been many complaints, it is something that needs to be considered. Especially when players are already flat-out stating this means they will (partially) skip the event. When event-quests start turning players away, there is something wrong.