really it's a function of all those shows being shot on the east coast and new york having far fewer shows in production than LA. They all have different casting folks tho, even the law and orders have different casting folks.
the funny thing is that the Law & Order franchise has all these "rules" about when you can do another show in the franchise after you've already done another (like if you've done L&O, how long before you can do SVU or CI) and how long until you can do the same show. Years ago, Dick Wolf was watching the repeats on TNT and in back to back eps saw one actor as the perp and in the very next repeat as a judge or something like that. Lol. there are more actors who have been in multiple eps than you realize. the more recognizable ones of course stick out more. Doing L&O is like a rite of passage for NY actors.