Not trying to defend it in anyway (you make very good points btw), but here's my understanding/TED talk on this matter...
In a weird way, the roots of this hobby are quite intertwined with piracy. When I first started watching dramas, there was no way to legal watch them. Everything was subtitled by fans and hosted on various third-party sites - even Viki (or ViiKii as it was first called) was originally a third-party platform. Even today, there's a lot of Thai and Japanese dramas that can only be enjoyed with fansubs. So for some, it's a habit - something they've always been doing (in some capacity) and something they feel relatively OK about doing (in some capacity).
While nowadays streaming services are pretty convenient, there's no one go-to service that will have everything you want. You got iQiyi, Youku, Tencent, Viki, Netflix, Viu, Kocowa, Disney+ as of late, and others that I'm definitely forgetting. The third-party aggregators collect things from all these platforms (plus fansubs too sometimes) and give you one spot to watch every drama for free. So for some, it's hard to resist that siren song, especially for younger drama-watchers and those who can't afford to subscribe. And of course, there's the people who simply just straight-up don't want to pay regardless lol.
