It might be something you're comfortable with not answering but the why of mostly to the Middle East seems kind of tough. That is, if the early Indo-Europeans were the mostly the people that the main theory thinks they are - early pastoralists identified with the Yamnaya culture who used wagons to become very mobile on the open Pontic-Caspian steppe and grow to a large population size there, and then from a springboard off that become very prominent in Europe and the eastern steppe and Central Asia as well (and then from the latter, rather in history later groups move to Iran and India).
It's fairly easy to imagine that some other people who didn't speak proto-Indo-European could come up with the package of wagons and open steppe utilisation before the Yamnaya, through some luck, perhaps emigrants from the Southeast European Cucuteni-Trypillian complex who seem to have been were moving towards the same package with more use of agriculture just had more fortune in making the necessary adaptations and won out, or proto-Uralic peoples who are in theory living in the close proximity to the same kind of spaces as pIE. But that only gets you a TL with total absence of the IE from history, not one with them prominent in the ME and absence in Central Asia and Europe.
What's tough is to see how the Indo-Europeans as the ones to first adopt how that package could have more of an advantage in the Middle East than in Europe or Central Asia. It's particularly tough because having that package seems central to what we identify as the core Indo-European culture - having cultural ideas that came from this relatively mobile open steppe pastoralist way of life (later subject to major adaptations and changes as they split and merged with other cultures), not just being some people who happened to use ekwos for horse and deywos for god, and perhaps had similar genetics, but lacked a culture on that root. (For instance one way to have the IE be prominent mainly in the ME is to have them transfer their languages to the more sedentary and advanced for their time Caucasian mountain cultures to their south, while not making it big on the steppe, and then go on a massive spree of having these Caucasian cultures be successful empire builders across the ME... but that's not really the IE as we understand them!).