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.
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