THE FOLLOWING IS MY OPINION AND HAS NOTHING TO DO WITH CURSE OR FTB
On a personal non-FTB, non-Curse level, I really don't get it.
Users want the client to be ad-free. Curse agreed. This means the client does not directly provide any income to Curse. So any development funds for the client are paid for using funds from products that do directly provide income to Curse. No Linux developers are volunteering to work for free. Which means a Linux developer would have to be paid the same as the Mac and Windows developers to develop for something that doesn't directly provide income. The reason the various launchers have the issues they have is they are relying on developers that are either doing this as a hobby, or are not earning much of an income. The pack developers earn nothing, the mod developers earn nothing, the launcher developers earn nothing.
I am not really sure where people, especially non-americans get this idea that things that take specialized effort ought to be provided free and the people making the product ought to do it out of the goodness of their heart. They should take 80 hours a week and donate their work, and live on air and flowers. Yes some people are able/willing to develop mods/packs/launchers as a hobby. And we see one of a couple things happen,
1. They get burnt out on the demands users put on their hobby and they leave.
2. They get offered a real job where they can pay their bills and support their families and either they quit the hobby or they have less time for the hobby.
3. Someone figures out a way to turn the hobby into something that earns enough income to make it workable and users go nuts about "perverting the free hobby".
And its weird cause it seems mostly to be something that occurs with technology and gaming. Like no one expects me to use my hobby for jewelry making to make them free jewelry. Or for a carpenter to build a house for free. But somehow coders are expected to work hundreds of hours without pay. And then people wonder why their tech degrees can't get them a job. That's simple, no one wants to support coders coding. People think nothing of spending 5-6$ on a book, but coders should never expect payment. Well in the real world, people need money for bills, food, shelter. Which means they are going to give their best effort to tasks that provide an income. For companies to offer an income to coders they have to make an income themselves. If a specific project a company does does not directly provide an income by itself, the amount of paid positions in relation to that project is smaller in number. And when the number of paid positions are lower, things like direct support for a operating system very few of the companies customers use is a much lower priority.
So you have options, you have the free launchers, that have issues because hobby coders cannot put as much time and effort into support, but they will probably support everyone. Or you have a freely available client that has paid developers that are supported by a company that makes money (omg evil) but isn't as likely to pay a developer to work on Linux for a product that isn't directly earning an income. I don't work for accounting, I have no idea how the funds work, but honestly if the decision were up to me and I had to make the call I'd personally say to put any income that could go towards Linux development into the funds for the rewards program for authors.
I tried releasing my packs on ATLauncher. It took 6 months for them to get back to me on packs that had been out on FTB since last spring. While I have no personal issue with the official Technic packs, I am not willing to put my packs on solder. I do not personally support the idea of easily offering people a way around mod author's wishes regarding their content. And saying "well we aren't directly hosting the projects, we are just providing an easy way for people to install projects other people host, therefore its not our responsibility to protect author rights" is lazy and dis-ambiguous. Its the same thing pirate bay and mega upload pull. I don't like it, and I won't support it even by association by putting my packs on it. I considered it, it would be easy enough. And I would get a lot more publicity/users. I am just not willing to even suggest I support that type thing. I don't consider other people evil or bad for doing it, I just don't find that it fits my personal ethics.
Contrary to the fairy tale world a lot of gamers seem to live in, most people reserve their best effort for things that can earn them a living wage. Not get rich, but be able to afford food and clothes and a roof maybe even walls. So basically, if someone isn't charging you for access, and they find a way to earn an income without charging you a fee, and it even makes it possible to get a better product for most users, why on earth should you be upset because your installation might be a little more difficult because you choose to use a non support OS? Are you volunteering to pay developers to support your operating system choice? Of course not. Users even get upset of mod devs have ads to get a little income from their hobby. Its free. No one is charging you for access. Quite frankly if my local grocery store told me I could get my groceries by watching a few ads, I'd pull up a seat and watch the ads and be quite happy with my free food.
These issues pop up on almost every game I have seen. And I really don't get it.