"The team at Arkane has been fully focused on optimizing and finalizing the PC version of the game. We aim to deliver the best PC experience to our fans and are hard at work to do just that." is statement given basically week to few weeks before games full release. After shitshow that was Dishonored 2 on PC statement like that from Arkane doesn't breath confidence about state of PC port.
This isn't the same studio that made Dishonored 2. Arkane is simply a brand now.
The real reason they didn't put a demo out is probably because of piracy. With denovo getting cracked faster and faster nowadays they probably want as long as lead time as they can on getting day 1 buys, and they want the core executable as inexposed as possible in the lead up to release.