Why game devs hate most key resellers?

We that love games are always looking for a good deal when it comes to buying games, we also know how expensive can our hobby be (in some countries waaaay more than others).
And usually new release games are the most expensive, so we try looking in the virtual stores to find if any offer a nice price, and I thinks than most of us came across an ad with an absurd low price for a new game.
The first time I saw a new game for less than 10 dollar I though it was too good to be true, and in a sense, it was. Let me explain why?

Given the news about Acid Wizard Studio, creators of Darkwood, making the game available to be downloaded for free, where are the reasons
This is what typically happen.

• The key reseller buys keys from a third party, and that third party usually used credit cards to purchase the game key.
• The key reseller allow a third party to sell keys in its website, like G2A that doesn't police this.

So what makes the dev hate so much those stores? The original credit card owners issue chargebacks, game seller has all money from former sales taken back, and is fined for each transaction (this is debilitating to smaller studios).
Each copy sold on G2A costs the developer money in multiple ways: key was obtained essentially for free, developer was fined for chargeback (lost money), and then you didn't bought the game directly (lost sale opportunity)

Due to the above, many developers would rather you pirate the game (no sale, but no fine) vs. buying from G2A, having to pay fines for the chargebacks (negative sales numbers for the developer). That's why they encourage you to buy from legitimate stores (Steam, Nuuvem, GoG, etc)