To begin with, it costs money to do interviews (transportation, parking, taking time off my current job, etc...) Not all interviews are in person, and taking time off does have a cost even in video/phone interviews. So there is a financial loss.
As for the 90 day limit, it doesn't say that the hiring has to be finished in 90 days, it's that the posting can't be open for more than 90 days. If it takes more time to finish the hiring process, than that is fine. And in fact, as you mentioned you are getting 10,000+ applicants a week, then you really shouldn't need to be advertising for more than 90 days as you'd already have 128,000 applicates in those 90 days. A few 10,000 more isn't going to help.
As for point 1, intended dates and realistic dates are 2 different things. An intended date shows a plan and purpose but can be changed with the proper information (aka, an extension.) It's not asking for a hard and fixed date.
Your second point is asking what the current market is offering, which can vary wildly, and requires those positions to be in demand to get a well rounded number. Not to mention they always show a vague number ($20-35, depending on experience). How these factors effect pay isn't explained, but when I can ask Bob/Dilan/Cindy++ "I see you've been in X position with Y years of experience. What is your current salary" is no longer hypothetical. The answers Bob/Dilan/Cindy++ all give me can help me better understand if I'm "over paying" my current employees and if it would be better financially to remove them for equally skilled employees for less pay.
As for point 3, you can get government money is you are "creating jobs". A ghost job posting fulfills this role without costing the company much. And there is other things to be gained by making it look like your company is growing, you can obtain better contracts "As you can see, we are a fast growing company, in fact we are one of the fastest growing companies in the area..."
Here are some sites that can help explain more about ghost jobs:
https://marketrealist.com/what-are-ghost-jobs-and-how-to-avoid-them/
https://www.thepennyhoarder.com/make-money/ghost-jobs/
https://builtin.com/articles/ghost-jobs