The US Open website shows about 370 entries as of this morning. While that is definitely impressive, I am surprised by the lack of titled players. I see zero GMs and only a handful of IMs.
Normally the US Open attracts about 10 GMs and an equal number of IMs (many playing in the shortest possible schedule). I really would have expected to see at least the Chicago based titled players.
Since GMs do not have to pay, does the USCF office have a list of free entries? If so, why are they not listed on the website? I know some chess players attend tournaments in part to watch their favorite GMs play.
The US Open does not draw as many grandmasters as it used to, because the prizes are relatively low compared to the time the event takes. I’m not sure the extent to which GMs are given an honorarium to play or a per diem allowance, either.
It is also possible that since GMs generally get a free entry into this event that the office has not yet entered in all of the GMs who have committed to playing. I can have Walter Brown check on that next week.
You are right that the prize fund has decreased a bit over the years. The 2003 US Open (Los Angeles) had $55,000 guaranteed (second most ever). This year seems to be $40,000 guaranteed, a 30% drop over three years. However, the cost to play in 2003 (minimum of six days plus travel to Los Angeles) was higher than the 5-day schedule in Chicago.
The 2003 tournament drew at least 15 GMs (I stopped looking lower than the top 50 spots in the standings) including several from Europe and South America. Considering that Chicago is home base for a few GMs, I would hope for at least 10. Understandably, most would play in the 5-day and 6-day schedules.