The difference between copyright and patents is that as a property right, copyright has a clear boundary: you know whether you copied someone else's stuff [1]. You can infringe a patent without knowing of its existence, and even if you do know and actively try to work around it, the only reliable way to determine if you are successful is in an expensive lawsuit.

Imagine if you wanted to put an addition on your house and needed to file a multi-million dollar lawsuit that could stretch over a decade before you could determine whether it would cross your neighbor's property line.

[1] There's still some gray area around fair use, but the contrast with patents is night and day.