Probably 80% of the software I've ever tried, I hated and never touched again. That's a bummer when you've just paid for it.
Paid software is usually a pain if you want to use it on more than one device, or when you upgrade a device.
Also, as to your original question of why people are reluctant to pay for software, it depends a lot on the software. Much of the software that people sell (e.g., a game for a phone) is less useful to me than a cup of coffee, so I wouldn't bother downloading it even if it was free. And even if your software is useful to me, it has to compete with lots of free alternatives that are very good.
There are also the security/privacy risks that comes with installing software from unknown providers. A widely used open source program would be easier to trust than an app from some random person on HN that I've never heard of.
That said, I do buy software that's useful to me. For example, I buy tax prep software every year, and I pay for e-mail (Fastmail) and a web-based RSS aggregator (Newsblur).