Plugin development, just like any other programming is working, even if it's not one's full time job. Wanting to get paid for work is only fair in my opinion. Ask your parents if they would still do their job if they didn't get paid, although we both know the answer. The fact that the plugin is free to download doesn't mean it wrote itself or took no time/effort to create.
Just like most plugins, TAB started as a hobby. With the plugin becoming bigger, the demand from users has gone up drastically as well. All the feature requests, bug reports and assistance requests would easily be enough work for a full-time job. Working full-time or anything close to that completely for free would be an absolutely terrible life decision. If I only spent for example 30 minutes a day on the plugin, that wouldn't even be enough to handle support requests, let alone actually improving the plugin.
There already are enough of "simple tablist plugins" on spigot which are absolutely trivial. Joining them would make this the 101st trivial tablist plugin with almost no features, which would be pointless to even do. Plugins that aren't trivial are abandoned with tons of open issues on github (such as NametagEdit or BungeeTabListPlus). You're just not going to find a plugin of such quality which is actively maintained, author provides support and plugin is completely free. Serious servers are looking for serious plugins and usually don't have a problem paying for them. This is the place to go, and is in fact much cheaper than getting a private plugin made, because public plugins "suck".
There are several ways of funding plugin development. The most common one is having the plugin paid. I did have this option in the past with free version available for trial. However, the free version apparently had too many features already that people didn't care about the premium version, because it didn't offer any additional features they would be interested in, again defeating the purpose of the premium version's existence. Users who were interested, could still get it from source code or blackspigot for free.
Another, even bigger problem was in providing support. Support was provided to everyone (with support for premium version only for buyers), which resulted in some free users abusing the tickets and literally spam them for every possible question instead of reading the wiki, wasting a lot of my time. Sometimes, people who got the plugin from blackspigot shamelessly asked for help with premium features, ultimately resulting in some people actually arguing with me that I should help everyone with premium features even to those who didn't buy it, because it's opensource anyway. At that point I knew I can't let this go for any longer.
Paying for support is still new to the MC community. Previously I only heard about it, but never actually saw any plugin applying it. This allows me to not have to deal with newbies who will shut their server down in a week due to their own incompetency, as well as give users a somewhat better reason to support my work. So far it's working pretty well. With lots of paid plugins you're going to have a hard time receiving any help, even if you pay. Here you have it guaranteed. This is probably also why it's working pretty well so far (although not everyone understands it, which is why I am making this article).
Another way is to make everything free and just accept donations. Users like this method the most, because don't have to pay at all, which implies that this method has the lowest income by far. It indeed does. I used to have the plugin completely free with donations available for 3 years and the amount of money raised from donations was absolutely smashed within the first month after introducing premium version. This proves that donation mode just doesn't work.
Not a single argument in your message makes sense.