I can tell you from experience from myself and my classmates that its not a clear cut rule that all 1st year guys should go to israel. If everything is equal in all areas, then israel is great for most guys because kedushas eretz yisroel is unmatched anywhere else. But the problem is that very often, not everything is equal. A yeshiva in the US might have better rebbeim for this guy, better environment, better controlled gashmiyus etc. In Israel, while many guys grow from the non learning activities such as visiting kivrei tzadikim, there are also many guys who get very hurt from the gashmiyus. This is mainly because there is a tremendous amount of freedom for a boy straight out of high school and since he doesn’t have the supervision which he has in the US, it can often spiral out of control.
Why does a guy need to go to Israel right away? Why can’t he learn in the US for a few years and then go to Israel if he so desires?
It is a tremendous mistake to think that every guy needs to go to israel his first year out of high school. It is terrible for some guys and the bottem line is that there are amazing yeshivos in the US.
You can argue and say that its good for a guy to get away from home. The answer is that there are many many yeshivos outside of New York which are amazing. A guy who goes to a different state for yeshiva still can come home a few times a year for bein hazmanim and his parents can still keep somewhat of an eye on their kid being that he won’t be gone for a year straight.