I don't get why WIPs without demos get so much hype... it feels weird when there are so many good playable WIPs that get less attention
I think it comes down to a few reasons:
Expectations of the readers
As much as we would love to believe a piece of work should get attention based on its worth alone, it's not really the case in reality. Like you said, there are many WiPs without demo that get a lot of attention, while other projects with a working demo/game who barely get anything.
This is a generalisation, there are completed games and demos that are widely popular, as well as WiPs without demo who get no traction.
So first, there is plain Luck. Luck in regards to who ends up seeing the post, who reblogs the post, whether it checks the boxes of whatever is trendy in the moment (genre/tropes/customisation/etc), whether followers are actively engaging with the post and blog (replies/reblogs/asks), etc...
You know: right time in the right place.
You can't really plan for that, even if you researched all the trends, where to promote your project, who to send your project to, etc... Still might not be enough.
What can help mitigate this is using marketing to your advantage, with actions such as:
teasing a new project to get some hype with for example: teaser posters, countdown to the intro post/demo, character reveal, lore reveal, UI teaser, quotes from the demo, playlists, etc...
having a compelling intro post, with a good hook at the start, a synopsis that gives just enough to get the reader interested, having nice design in the graphics, including relevant links (demo, forum, tags, etc...), including what the game will feature (or what it already has), tagging the post properly (#interactive fiction, the genres, customisations, type of game, the system, etc...)....
submitting your intro post to directories, or promoting on different platform
continuing to be active on the blog after the intro post/demo drops with snippets, answering asks, and pretty much again what was in the first point....
Does this seem like a lot? Because yeah... it is. And it's not always feasible to do all of this. It requires careful planning, and skills, and knowledge. (I can draw to save my life for example...) And it can be very very frustrating to having done all of that and get little interaction (and the luck part comes back into play here).
And finally, reader expectations (I am not sure whether it is the right word...).
Hype can be a double-edged sword. The more you have, the higher the chance the end result might not match the hype expectations (I would loooove to know how hyped project continued in terms of interaction after a demo drop).
When you don't have a demo, people can only learn about the way you write or the character or the story from what you publish on your blog. As much as snippets can give you an idea, it's still not the actual thing. So you can't really disappoint people just yet.
Until it is set in stone by a demo, Reader's imagination can run wild (and even to the opposite direction of what the author intends).
There was that ask a year or two ago sent to an author, complaining about the amount of snippets they had written or asks answered, when there was no working demo yet. The reply of the author was suuuuch a good one, but I can't find it ;-;